As I pointed out, a Class 10 is 1/5 the speed of a SATA III SSD — doesn't matter how it's hosted on a 2012 or later Mac. That's slower than a 5400 rpm HDD. If Class 4 or 6, that's even slower.
If fast enough, then great, I suppose. Only the small ones are inexpensive. Above 128GB, they become expensive for what you get.