I have flown a C 210 with the Robertson STOL kit. It has a significantly shorter takeoff run and you can fly the approach at C 172 speeds. In fact you have to or the aircraft will float forever before touching down.
Roll control is still pretty good even at low speeds and in general the system works very well.
The only disadvantage with the mod is that the maximum flap extension speed is reduced form 165 kts to 110 kts. This is a PITA for flying IFR when ATC wants you to keep the speed up.
The only other issue is the aircraft does not like unpaved runways. There is a lot of weight on the small nose wheel so it will dig in on a soft field and it is easy to damage it on rough fields.