I've driven both, I started with a mugen, great buggy mbx6. About two years ago a bought the SE version and loved the way it handled. Then I went with a losi, worst mistake ever!! Left racing for about 8 month. Started again with a mbx6r, car handles great but not aswell as kyosho. Now I have both but I couldnt justify the price of a kysho so I bought it used off of a friend. The SE version I had was so cheap in quality that it showed much more wear than my 1year 1/2 old mugen vs my 3 month old kyosho.
The difference in handling was that I felt the kyosho more connected to the ground and had alot more consistant turning, the rear didnt feel bouncy and loose like the mugen.
Mugen is very good buggy but the kyosho has a slight advantage in handling.