So I find myself often making comparisons between the Miata and my S13s.
I must say, I much prefer swapping slave cylinders on my S13s. I can do them in ~10 minutes. Don't even have to jack the car up.
The Miata, on the other hand, you gotta get it in the air, take the passenger side wheel off, and then the cross member subframe pieces are all up in your way, and you have to finagle your hands around them. It also has a damping loop that seems to put a sideload/pressure on it, so its difficult to move it into position to put the bolts back in that hold it to the trans.
That being said, its still better than most American slaves (where they put them INSIDE the trans). I would hate having to pull the trans for a stupid $20 slave cylinder.