The new NFA/Joe Bob's 9mm glock lowers really got me thinking about building a 9mm AR.  
Curious to what the opinions and experiences are on the PSA AR 9 uppers.

I'm really thinking about this  upper for an AR 9mm pistol/pdw build.  

http://palmettostatearmory.com/index.php/ar-9-ar-47/ar-9/psa-10-5-9mm-sqr-9-upper-with-bcg-and-charging-handle.html

Also, anyone know if their 9mm BCGs are good to go with the glock style lowers or if I'd have to get the bolt modified to run properly?

I'm not positive but I don't believe their BCG is glock cut.  When their 9mm stuff first came out there was some talk of a glock lower coming out, but it appears to be vaporware.

You'll need to have a PSA bolt modified to work with a Glock-type lower.

That's pretty much what I was thinking but was not sure.   I know that there is someone on the forums here that will do that modification for a very reasonable price.

Any other potential issues with that upper on the glock style lowers?

I think the guy's name is 'Mad Machinist'.  Everyone seems thrilled with his work.

That said, any reason why you don't just buy a $140 New Frontier modular bolt?  That's prolly the cheaper way to go after all is said and done.   I have one in my Spartan 9 Glock build, I just built it and only put 10 rounds down the pipe so far but it ran like a clock.

Yeah, the NFA modular BCG certainly looks promising.  I was just figuring, depending on pricing, if the PSA complete upper is the better value and then getting the bold machined to a glock cut may cost less than piecing together an equivalent 9mm upper.  BUT, if I can build the upper piece by piece for less that may be the route I'll take.