I just think a person is better off running x39 in a rifle and mags that were actually designed for it, reliability will be much higher and a low cost rifle running corrosive ammo is a much more forgiving platform if the owner gets lazy on the cleaning. Do a bad job cleaning an XCR and you could be looking at a heafty bill to get it running again.
I feel the same about Norinco 5.56 ammo, why spend $2000-$3000 for a high end black rifle then feed it garbage. There have been so many threads started with guys having problems with it I can't believe anyone would still run it in anything other than an M-4gery.
In the end everyone is of course free to do what they want and this is just one guys opinion.