Thought I would start the talk on the new mags from ETS. There are a couple of things that they have over the Magpul mags IMO.
-Able to use any Glock OEM baseplate, or aftermarket baseplate/mag extension.
-Factroy 140mm USPSA/Multi-gun legal mag.
The other arguables that give it a potential leg up are that its translucent, and cheaper than an OEM mag; especially when considering buying mag extensions and an OEM mag. I have pre-ordered a couple standard G17 and 140mm mags from Rainier Arms (link below). Obviously a downside to using a 140mm factory mag is that you forgo the added weight that a mag extension adds and can aid in dropping free. If the mags seem durable and good to go, I might try adding some lead weights into the bottom. I'll have to see when they arrive. For a guy getting started into multi-gun I think they would be a good purchase. It will give you the added capacity to compete with fewer reloads, cost far less than the standard extended setup, work well as a USPSA Limited Division mag if you don't stick with it, or like to train in that discipline when there are no 3 Gun matches. They are releasing a standard capacity G19 and G17 mag along with the 140mm and 31 round magazines. Links below to the Rainier pre-order for the curious.
Glock 19 Standard
Glock 17 Standard
140mm Mag
Sub-gun/31 round mag
ETA Picture for the other kindergarten level readers like myself.