To be honest, The Orion Wasp CRF Rev .21 is my first experience with a engine that use a Picco case and Carb (the guts are completely different). I have noticed a small problem with the carb, it seems to lean out when the fuel tank gets low, just a minor problem thought, a little lean bog, I was told that the picco carb leaks air when they are hot, I've sealed the carb but haven't had a chance to run it yet. Other than that it's a breeze to break in and is relatively easy to tune.
The GRPs (I've had several Ninjas) can be a little tricky to tune sometimes. They seemed a little more sensitive to weather changes.
The Novarossi 21-5K holds a pretty good tune
Keep in mind every engine has it's characteristics, you really can't go wrong with a good brand name from Italy or Japan