that is a serious difference in price vs the canon.
7.4V that is how much power it is putting out, and the reason the canon (and all other manufactures warn about using 3rd party) not saying they are correct in their warning but this is what can cause problems.
1500mAh is simply how long it will last. Normally on external attached batteries it is not a big deal because the batteries are just bigger, but with internal batteries you have to remove more of the inert material so more capacity in the same space may mean more heat.
These are just theories of mine so take them for what it’s worth.
I have used 3rd party batteries before and never a problem. But never send in a camera for servicing with a 3rd party battery in it. Even if the issue is not power related the warranty can be voided.
FWIW, my son does research in the battery field and he buys 3rd party batteries.