Yep, I’ve seen drives that are 100% green on SMART and self tests but operate slow as dirt. Although, of course, you’re going to want to make sure that it wasn’t the cable or something.

I guess if you check it periodically, like once a quarter or year, it would be ok. It might not effectively be too different than a HDD since you have to check that periodically too, but more often checks might be warranted due to aformentioed points in this thread about flash data retention and MicroSD reliability.