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.

Most I would do is a write test followed by a read test, and then check the smart counters