Low quality (which might not be a big deal since you can swap), low capacity, slow phone charging, expensive.
But they are convenient.
They (FuelRod) did succeeded in creating a solution(battery swap) for a problem(crappy product) they created. Sounds pretty genius to me.
Especially since (according to their website) there are only 77 locations in the US to swap....
For $30 you can buy a battery pack that has 5-10x capacity and can charge multiple things at once.
I guess these are good for an "omygod!ineedacharge" situation...or for those who don't know about online retail.