Kits can be very reliable if you treat them well. Break-in is the most important. Be patient. If you know you cannot be patient, up-jet a ton so you can't ride fast and lean for the first 200 miles or so. Running too hot, too fast can make your piston slightly oval. Then it won't seal well in the cylinder and won't transfer heat well... next thing you know you have blow-by and your rings are toast. The rest is a catastrophic meltdown. Some may say that they didn't do a proper break-in and their ped runs fine... but how many have gotten 10k miles out of their cheap Airsal kit running 40-45mph on a regular basis.
I run the 14/12 carb and it does just fine. The 15/15 didn't do much to increase performance.
-Eric