Motors will function fine at 12s. The increase in RPM only comes into play when you’re talking about systems reaching the 20s mark.
Flipsky uses cheap parts and takes no precautions to harden their motors, so unless you want broken magnets and losing money to pay for MORE motors, I say nay.
As for alien power, their motors have been known to be hit or miss. If it’s a miss you’ll end up with a motor you can’t use, if it hits you’ll have a motor that can serve you for a few years if you treat it properly.
Personally I reccomend Maytech motors if you’re EU, as they seem to have better reliability than other vendors.
If you’re in NA, I reccomend Torqueboards. They add (small amounts of) epoxy to strengthen them from vibrations and impacts. These are the best motors (for the mass market) that your money can get (from a reliability/cost/performance perspective. I don’t think I’ve seen a TB motor arrive broken or fucked up in a long time, and Dexter should be given props for that.