So I've decided I want a 9mm "smg style" pistol. I want it to be reliable, have a last round bolt hold open, and have AR style ergonomics/controls. I would prefer a side charging action and It would be nice to have it take glock style mags.  I've done a little bit of net research and haven't found the "go to" build combo for 9mm side charging glock mag ARs.  It seems reliability and last round bolt hold open are a bit up in the air when building your own. So I've sort of narrowed it down to 3 options(feel free to recommend something else):

1.  CZ Scorpion - I don't like the proprietary mags and lack of AR part compatibility but the price is right and it's a turn key solution.

2. SIG MPX - Again I don't like the proprietary mag.  It also doesn't have a side charging receiver but it is a turn key solution and I generally think of SIG as having higher quality products.

3.  Build my own. This option obviously gives me the opportunity to get every feature i want. I have read the reliability and LRBHO feature can be questionable with the DIY setup, at least it seems that when people discuss their builds, they really stress the point that the LRBHO actually works and they can run different ammunition with no issues. This makes me think it is not the norm. I was looking at quarter circle 10 lowers with perhaps a gibbz side charging upper but havent been able to really find write up that explicitly says "this is what you need to buy to make this work".

So what are your opinions?  If you think option 3, please tell me what specific combo of upper, lower, barrel, bolt, buffer, spring, etc have worked well for u or for someone you know.

Let's assume my budget is approximately $1500 w/o optics.

I think most of the builds with the Colt style mags can reliably last round hold open. I just built a 300 pistol using a side charger. I really got interested when I saw the Matrix design where the rail doesn't extend behind the receiver when charging. Matrix has been hard to find in stock, then I saw MAS carries what seems to be an identical design. Well they are constantly out of stock too. Then XProducts recently started carrying the same upper receiver. I got the Xproducts version and I'm happy!

I got some rail section coming so I can move the light to the bottom and a QC connector for the rail so I can have a 2 point sling mount.

That's kinda cool.

I want a side charging 9mm with Glock mags as well. I can't afford it for now, so my research is somewhat limited, but everything led me to new frontier armory for most of the gun, and most likely a ballistic advantage barrel.  There's a picture floating around here somewhere with a wilson combat TRIM rail on a similar setup, and it looks bad ass. I think it had HK sights too. It's what piqued my interest in them.  I have no idea on BHO, but the side charger would make that easy to deal with.

Quarter circle 10 gets mentioned a lot as well, but new frontier has a lot of love, and a good selection.

I would much rather build, especially on something like this one. There isn't a whole lot offered outside of building, and you can wind up with a badass gun if you want to spend the money.