If these additions add mag capacity and work without fail, that's great.
On the other hand, I regularly use CZ75B 17-round mags in my P-O1 and Masada Slim without any sleeve to fill the gap between grip and mag base and have no problem. Even with my big hands, the bare metal doesn't cause me problems and I can't say I've ever even noticed the gap.
Nonetheless, for those who wish to use them for the additional capacity and aesthetics, it appears to be a nice feature.
I recently installed Hennings 2-rd extensions on my 97B mags giving me 12+1. 12+1 in a first-rate shooting pistol like the 97B is something I can recommend.