I stumbled across a preowned but unfired G19.5 MOS a few weeks back that came with an SLR magwell and Ameriglo suppressor sights for $600 shipped so I snagged it thinking I'd probably not like the magwell and dump it and the sights, but I actually really like the magwell so far. I haven't shot it yet to see how it behaves there, but I've done a couple hundred or so draw and dry fire strokes with it and I love the way it index's each time. I'm personally not a huge fan of the glock grip angle since I like being good at shooting other pistols too, but the magwell with my pinky on it and the way it ever so slightly rotates my hand a little makes it feel like a normal grip angle and feel really good too. It also allows me to get my whole pinky on it with the slight length it adds.
This is my first glock with a magwell though I have had dozens and dozens of them that haven't had them, but I don't think it will be my last. I need to carry it some with the magwell to see how it prints and also shoot it at least a few times before I order them for my other 19's.
I can't comment on the others, but I can tell you that the SLR is at least dry fire reliable, fits very well with no slop, appears to be a very high quality product as you'd expect from SLR, and my dick beaters are happy with ergo's.