I installed one (of my two) of AIM Critical Defense melonite ($39) LPK's today in an Anderson lower receiver. My thoughts on it:
I LIKE this kit. It is a fantastic bargain! I always change the grip anyway, and use lowers with built in trigger guard, so this kit is by FAR the best value out there for someone like me.

Pro's: Everything was in the kit (NOTHING was missing. I hijacked a take down detent from spare parts because I couldn't find one, but later found it hiding in the buffer detent plunger).
         Everything works as it should.
         Trigger is good (not great, but very decent for a "mil spec" trigger).

Con's: I don't know which parts are supposedly melonite... but NONE of it looks melonite to me. I've used numerous melonite parts (barrels, RE plates, FH's, Castle nuts, etc) and ALL of these
           parts look parkerized to me. It not bad looking, but has the usual dry/scratchy look of park (Trigger, rear take down pin and selector lever in my pic are representative of ALL the parts in
           this kit).
          Safety spring (and/or lever) is unusual. It operates smoothly and crisply, but is above the normal tension (force required to operate). I use the same MP K2 grips on ALL of my builds, so I
          know it's not a grip spring hole depth issue. Either the spring is a tad long, or it uses a slightly different selector lever divot set up.
          Magazine release button has cosmetic flaws (minor chips and silver color spots( which I touched up with Alumablack.
          This brings me to oddity #2.... the selector (safety) lever itself. It is not the usual "mil spec" that I'm used to. I'm used to levers that have the serrated grip section cross the entire pivot
          (well actually more like 3/4 across the round pivot section).
          This lever has a "post pivot" lever (the serrated grip portion starts AFTER the pivot area.
       
          Pic of selector lever and it's "off hanging" grip section (unlike any lever I've used before. Almost looks like a very old design):




Pic of the cosmetic blems in the mag catch button and the obviously parked (not nitride) hammer (actually, as I've said, NONE of the parts appear to be nitride):



I may wind up clipping a few coils off the selector lever spring, but all in all, this kit is one HELL of a deal! Although I was expecting a shiny (or flawless deep black) nitride/melonite finish (which this does NOT have).... it's still GTG. Basically a low cost, quality, minimalist LPK that WORKS and has ALL of the parts in it! I give it my approval
Nice job AIM! Thank you for offing this!


ETA: This is what I mean by what I'm used to (for selector lever). Notice the grip area extends to the center of the pivot point. This is a PSA selector lever (same as any other lever, other than AIM's CD, that I've used):

Thanks for the review! Now clip your finger nails

Oh dang it!... I was hoping that wouldn't show! Be glad I kept my toenails out of the pics... they're even worse!

Are you referring to the "Critical Capabilities" Nitrided Essentials Lower Parts Kit listed (currently Sold Out) at AIM? They don't have a "Critical Defense" LPK. Assume you're unintentionally mashing up Critical Capabilities and Hornady Critical Defense. Thank you for the review, btw.

I bought a couple of the Critical Capabilities LPK's a few weeks ago. BOTH FCG's went full auto after safety testing OK ... I'm waiting on replacement parts now.

Edit: One went full auto, the sear wouldn't engage after testing OK. I put the FCG from the 2nd kit into a lower, and the sear wouldn't engage at all. The rest of the kit was great. The FCG out of them scares the crap out of me now. Also, one of the kits was missing the disconnector.

I had a similar experience, first of all the parts really don't look Nitrided as the OP stated. Once you get the oil cleaned off they look parkerized. Mine look the same way, so its a bit doubtful that they have the same quality of coating that most users are acquainted with. Secondly, my FCG group also went FA during a function check. The trigger was so grainy/gritty anyway I tossed it aside and went with a ALG QMS for a few bucks extra...

Everything else about the LPK was great... including the price.

I don't bother with the stock parts kit triggers anyway. Just the essentials. So many affordable options of quality drop-in triggers out there now. I just installed a Velocity 3lb Trigger into my current build. Cost $129.00 and arguably every bit as good as its $300 competition.

Typical low tier junk.

Same thing happened with mine. Disconnector is out of spec. Disco spring also looked weird. Replaced both with some parts from the junk bin- works fine now. Anyone with one of these LPK's better do a function check ASAP.
I'm detecting a trend.

Melonite is a metal treatment, not a coating. It chemically alters the metal. That being said, those do look like the typical finish on GI parts.

PM me your order number and I can get CC to send you replacement parts.  If anyone has any issues with them, we will get it taken care of.

I had the  double tap issue resolved awhile back. Aim and CC took care of me...

On a side note if you bought a lpks watch the mail I had a padded envelope with a disconnect in it..

And for the safety selector it's similar to the dpms one

I got a disconnector in the mail from CC yesterday. I figured it was just the one that was missing out of my kit.

Just to keep you guys posted, I put the original FCG back in with the new disconnector I received the other day. It tested perfectly. The trigger reset strongly, with the sear grabbing well. I can't say I'll ever completely trust it though.

Yes, sorry... I meant "Critical Capabilities".

Mine function checks fine, but hasn't been run yet. I'm hoping I don't have the issues some others had! I'm also glad I'm not going crazy and that others question whether this kit is really nitride as well (I'm convinced it's park, not nitride).
Thanks for the feedback guys!

Also, just a thought.... if disconnector problems seem to be common with this kit, AIM may want to proactively "recall" or contact all buyers and offer replacement part BEFORE more issues happen. Going full auto is "kind of a big deal". I know, for certain, that it would instantly "lifetime ban" me from one of the ranges I currently use. I've had the "double/full" tapping issue with an AK fcg before, but fortunately it was on private property, and I only load 3 rounds for any first few magazines during a test of new parts. Others may not be so fortunate or cautious.
Just a suggestion (for trial runs, AND perhaps how AIM may want to handle this).

When I had my issue a few months back I posted it on here to make others aware to function test every build and AIM contacted CC and CC had a replacement out to me the next day.  

Discos can wear over tone  It's always a good idea to function test and practice firearm safety rules

UPDATE:
Took it out for a run today. Ran flawlessly with my small shooting sample of 100. Hoping it stays that way! But so far... I still think this kit was a HECK of a bargain (though I'm still let down by the park look and overly stiff safety)!! The trigger also felt as good as any mil spec trigger I've used.

Ah!  The ones I bought also had hammer-follow after install during my safety check.  Once I replaced the disconnector with a spare I had from another kit, it worked fine.  



 

UPDATE #2: also clipped 2 1/2 coils off the selector spring which brought it to the same resistance as my other safeties so it's all good now. No malfunctions, no FCG issues, no selector tension issues (since mod). All is working smoothly, and with proper feel. I'm a fan of this kit!

I usually do the captured spring for the safety so I trim the spring as needed if to firm