It works like a hardtop, You can keep your soft top underneath, but you can't use it at the same time. Or you can take it out to save weight. I'm sure this is a bit more work to remove than a standard hard top, I believe it's meant to be kept on most of the time.

The soft top is taken out with tools. Specifically a 10mm wrench and socket among other things.

 

Does not work with convertable Miatas, only coupe versions. Top must be cut off.