Does anyone have any experience with either of these aluminum magazine extensions? If so, how would you rate them?

The two seem to use the same system, with the only difference being that the grip cut outs just above the bottom of the base plate are a single large one (Shield Arms) or two narrower ones (AIM Surplus). Otherwise, they appear to be identical (or almost so).

Are they are a good choice to "enhance" my SHTF FML G17 mags?