I'll be ordering 2-3 metalform mags to cover all my bases on the 9mm platform.  It seems the different models have to do with feed lips and followers.  I know a few of you use these mags.  Can anyone make a recommendation which model would work best with my RRA blocks?

Thanks for your input.

9-SMG-32-P    
9-SMG-32-S  
9-USMG-32-P  
9-USMG-32-S

Me too.

9-SMG-32-P = flat lips, plastic follower
9-SMG-32-S = flat lips, metal follower
9-USMG-32-P = upturned lips (like an Uzi mag), plastic follower
9-USMG-32-S = upturned lips, metal follower

... and does anyone know if an UZI mag can be made to hold open the bolt with a metal form follower?

where are you ordering from?

Plastic follower or metal follower is user preference and flat lips.  I have NO functioning problems with both followers and flat lips.  Upturned lips in an UZI thing.

UZI mags do not have the channel on the back for the BHO.  It takes a piece of .010 spring steel welded to an UZI follower to work.
http://users.zoominternet.net/~picplace/bolt_hold_open.htm

Don't get the cart before the horse. I am working on better pricing with Metalform.

Thank you for your answer regarding the follower.  I just modded an Uzi mag (I have no other mags, period) so I can now see why you'd need thin spring steel to actuate the BHO.  I can also see that I'd rather have some metalform mags

One good thing about converted Uzi mags: they are made from really thick, hard steel, I think they would last forever in normal service.

Order direct from Metalform - > HERE

I use the 9MM-SMG-32-P - these are basically the same as the Colt marked mags of the last few years - blued finish, std feed lips and polymer follower.

The 9MM-SMG-32-S are basically the same as the older, preban Colt marked mags that had metal Uzi-style followers.  Only difference is the old mags were park'd finish and the new ones are all blued finish.

I'm not sure on what benefits Metalform saw with the upturned feedlips, so you may want to call them if you want more info.

This is what I was looking for.  Thanks for the info.

It's the same thing I've been saying for the last few months.