I'm pretty solid on doing a colt mag build.
1 - there seems to be no proprietary mag release
2 - LRBHO seems to be a bit more reliable
3 - magazines aren't expensive at all
4 - a $50 lower + $100 adapter is $100 less than the dedicated lowers I've seen with the exception of the PSA Glock lowers that don't have a LRBHO.
1. There is a 9mm mag release that works a little better in some cases.
I recently switched to one because I have one mag that the mag catch barely held the mag in place. With that one mag, it would just all of a sudden just drop out and land at my feet without rhyme or reason or warning.
Since I have replaced the catch with this, it seats a little deeper and the mag and work better.
http://stores.9mmar.com/spikes-tactical-mag-catch-9mm-only/
or
https://www.rockriverarms.com/index.cfm/fuseaction/product.display/product_id/5819/index.cfm
3. magazines run anywhere from $10-$32'ish each depending on which you like. Most all of mine are converted uzi mags because I already had a bunch of them. And converting isn't exactly the right term I guess, but I had to mill the notch for the mag catch in the bodies. Took all of a couple minutes each measuring them and then taking the spring and follower out so I didn't cut them too. They don't hold the bolt open though. Other mags like Cpro and ASC, Colts, and metalform will lock back when empty.
Personally, I don't mind it not holding open and it isn't a huge deal to me. I would personally hope to never have to expend an entire 32 round magazine in the first place. But I see the appeal of it I guess. In reality, I have more guns that don't lock open when empty than do. So, I don't pay much attention to it.
4. I think I have about $210 tied up in my mag block and Anderson stripped lower altogether. At the same time, they didn't have the glock conversions when I was doing mine. I have also seen Sten conversion mag blocks when sten mags were dumped on the market for cheap. And there was a company that made a mag block for Unmodified uzi mags if you could find one on the used market because I don't think they're in business anymore despite the blocks worked great.
I also don't have any glock stuff, so I'd have to spend out more buying a bunch of mags too so that too is a consideration.
I don't necessarily think either glock, colt, sten, uzi, or whatever style is better than another really. Just a different route to get to the same point. The only exception maybe would be glocks have drums. But I'm not a big drum mag guy anyway. I can usually buy enough stick mags to have double the capacity of a drum for the same cost per capacity. But, that's getting into a different subject altogether.