By the way OP, have you considered mags? Here was a video on YT about using actual Glock mags. There is a dimensional difference that affect the functioning of the slide lock. Just FYI. I believe they were talking about the Gen 5 mags. I have not had any problem with Gen 4 mags.
KCI
I bought KCI mags for mine and they function fine. They are the closest to the OEM Glock mags. They all function fine for me. I got a 10 pack for $101.00.
Amend2
These are light weight and seem to a little more robust than the Magpul mags. No witnesses holes though. I bought a 10 pack for $70 and change.
ETS
Work great and cheap. I paid $7.49 each for them. I have 3 15 round and 3 32 round.
MecGar
Steel 18 round mags. I bought 3 of them at $17.00 each. They fit better in an actual Glock. They are a little loose in the RXM. I would not recommend these for the RXM. They are all steel, no polymer on the bodies.
I haven't tried the Hex Mag carbon fiber yet, but when they come back in stock I will order some. But I am going to try those carbon fiber ones in my 19X first, as I don have many range mags for that one.
I also have 5 of the Magpuls. I found them to be just OK. I have 34 mags altogether to share between Glock 19 and RXM. You can never have too many mags though.