I used fast frames a lot when I worked in the embroidery shop. They worked great. Just as the name implies. And I do believe they will put together a package that suits your needs so you don't end up with sizes you have no use for.
I have a BMP8 with Fast Frames, and love them both. It took my awhile to realize I didn't always have to use sticky stabilizer with the FF. Once the design is centered, I now just use clamps to hold the blank on. BTW - if you don't want the sizes that come in the FF package, call FF directly and their Customer Service specialists will help you put together the sizes you need. Price I found is the same.