Do you mean one of each? Or are you referring to some new product or something? Many of us with reiners use leg boots as well as bell boots-other disciplines do too. I am not really sure what you are asking.
I use SMB II Medicine Boots & Bell Boots on my young mare. She has a tendency to spaz out & throw her legs all over the place - I'd prefer she not catch herself while doing it. I'll also barrel race my gelding in splint boots + bell boots (or polos).
Are you considering using them for a certain reason? They're not really necessary if you're just every day riding or not doing anything extremely stressful.
Bleck. They just look cheap. Also don't look like they would fit correctly. If you're going to get something like that just spend the extra $$ to get separate items. You can get them separate for less than that.
Wintec Splint Boots $20 (surprisingly they've survived 3+yrs) + Davis No Turn Bell Boots $10 (clearanced at STL) = cheaper & better deal.