The so called "universal" and/or "unifit" adapter handles are generally crappola. They use little set screws to adapt, and are notorious for always being loose and floppy. Most important, they ONLY work on basic 2/3 handle tubs and showers.....separate hot and cold faucets. There is NO generic replacement for your handles. You must get specific "made for Mixet" handles. You will find chrome, clear acrylic, and smoky acrylic. You might find some satin nickle. That's about it.
Mixet valve bodies have know defects with crossover, so if you have a water recirulation system, you should either replace the valve now, or gt the NO-MIX cartridge, about $100.