There are lots and lots of pretty fish that don't harass each other to breed constantly already available on the market. Heck, that's why male guppies outsell female guppies. Hybrids are a tough sell for most people unless they are fantastically gorgeous with nothing comparable available. From what I can tell, muppies aren't that pretty, certainly not prettier than the source stock. Most people who get livebearers do so because they want fry--otherwise, they get just males. No need to get hybrids.