If a gun company recommends the use of aftermarket magazine assemblies that extend factory magazine capacity, I'd give it a serious look.
Until such time, I'm conservatively cautious. (Hell, I was conservatively cautious even using factory-provided "+" magazine extensions on my G27 mags back when I was able to buy factory-assembled "+" extended G27 mags.)
I like as much optimal reliability in feeding as is possible to achieve, and I'd willingly give up having 1 or 2 extra rounds of added capacity if it meant maximizing reliability.
A little while back some of our guys (at my former agency) were using aftermarket magazine extensions on a couple makes of pistols. They weren't prohibited. (Think different guns using plastic and metal magazine bodies.)
One day one of the guys had repeated feeding stoppages occur with all 3 of his modified magazines during a qual course-of-fire. He was using the same provided ammunition that worked fine in everyone's guns and unmodified factory magazines. I was told that inspection of the magazines indicated possible issues involving the extensions having been added.
Sure, I knew one of the other armorers who has not had any problems using his metal extensions on his metal-bodied magazines, but as an instructor and armorer he's typically also very careful to constantly confirm the condition of his magazines as assemblies. (Magazines are assemblies of parts, you know.)
Last I heard, amidst some grumbling by some folks who liked extending their factory hi-cap mag capacities using aftermarket products, the use of aftermarket extensions are no longer authorized on duty weapons for anyone. Folks can still carry an extra magazine or 2 (above the usual 3 issued ones) if they want to increase their ability to carry more ammunition.
Choose where you're willing to risk compromising with your pistols used as dedicated defensive weapons.
Game guns? What's the degree of risk exposure? You risk losing points or a match. No biggie, as nobody's trying to kill you.
I also look at it another way ...
The engineers who develop the specs for the magazines being used in the guns they design may invest a lot of hours and R&D testing with the magazines provided with their pistols.
How many hours of testing do the engineers who have designed the guns do with aftermarket magazines or magazine extensions? How many of the gun company engineers make recommendations about the use of aftermarket magazine extensions?