I've ran the .49 and .77 MVVS engines with very good success. Yes they have midrange problems, but that comes down to mixture adjustment and back pressure. They like a little extra back pressure compared to some engines.
They run well with no or low nitro, 0 to 5%. That's the way they where designed. If you want to run higher nitro content fuel you'll need to add some head shims.
Morris Hobbies gives good customer support on these engines. At least they have for me.