I have sparred, full contact with mixed martial artists. I used mostly JFJKD techniques vs MMA stylists, but once in awhile, I would mix in some old Kickboxing techs. One thing I found, is that these orthadox fighters were a bit clumsy with thier feet when I would circle right (south paw). I also found that it was much harder for them to throw round house kicks while side stepping right. I'm not really a "grappler", so I found that the transition from stand up, to clinch, to ground was dangerous. I felt like I was going to hurt myself trying to stand up and wrestle. I usually used the grappling techs that I was being taught in that class, when I was on the ground... however, I saw many openings for groin attacks while in the gaurd, during sparring.
It's a good experience to sparr, full out, with Mix Martial Artists. I've learned a lot. I used to come home with some nasty rainbow coloured bruises all over my shins and forearms. ha!

The Frank Shamrock clubs are hard-core!