I’m looking to pick up an AR9 that utilizes MP5 style mags (sorry, I do not love the Glock mag look). This will be chambered in 9mm with a 6.5” or so barrel length. This will be a home defense/truck gun that will not get used much, it’s a ‘just incase’.

So, should I look for a Sig MPX or one of the other AR9/MP5 variants like Wolfpack Armory, New Frontier Armory, etc???

If you decide to go with a Sig Gen 3 MPX, I would sell you mine. It is unfired.

Send me a message with info

Can you legally buy a MPX in New York?

As far as 9mm PCC's I have a Vector (Glock mags so that's out for you), MP5, and just got an MPX this week. My favorite so far is the MPX, it's awesome... so that gets my vote. Having to pay $59 for magazines is not awesome.

Even so, MPX is still way cheaper than MP5- which did NOT come with a brace, optic mount, ambi charging handle, or last round bolt hold... all of which DID come factory on my MPX. Also, MPX ergos and reloads feel more natural coming from AR's.

The only others I personally know of that don't take Glock mags aren't AR9's- the Scorpion and PSA AK9... Although I hear bad things about Scorpion mags and also I don't live under a bridge so there's that. Just kidding... All jokes aside, I would try the AK9 over the Scorpion... because I'm not gay.

IMHO, the MPX is a terrible suppressor host...gassy and LOUD.  
https://www.ar15.com/forums/Armory/CMMG-Banshee-300-9mm-/48-518476/

If you aren't going to suppress it then they are fine.

The MPX screwed the pooch when they decided to attach the handguard with only slip fit inner rails and a pin.

Lots of choices for scorpion mags that don't crack like the originals. CZ even makes a second version that works great and does not crack.

My MPX is amazing. The removable handguard is a fantastic invention despite what the guy above me says.  I remove the 8” barrel for cleaning, I put a 16” barrel in for USPSA, and it does suppress well.  After thousands of rounds through it, I find it wayyyyyyy better than any MP5 variant I have been issued or used.  It just is t quite as iconic as an MP5 in terms of looks.

Beware, it does require more cleaning than an MP5, and it is very hard on triggers that are not designed for it.

Have you looked into the Quarter Circle 10 options?  They have "AR9"s in all of MP5 mag, Colt Mag, and Glock Mag varieties.  Uppers swappable among at least the MP5 and Colt options.

I would NOT buy an MPX (or a P365, or a 320, or the new Sig Cross that has been recalled).   Patterns of behavior.

Have had several AR9s a MPX and 2 Scorpions.  I don’t own any of those at this point .  I now own a PTR K and a Zenith Z5 Mp5 clone.  I wasted money IMO on not going this route from the start.   I shoot suppressed and the MPX is horrible in this role. The scorpion is like a howtzer vs the mp5 In the recoil department so follow up shots suck.
The CMMG guard setup has my attention but I haven’t been down that road yet.

DDLES Colt pattern lower