maybe a little more noise at startup. you have to make sure it is warmed up before romping on it but you should do that anyways. usually cheaper. Just inspect the cylinder coating. the kaw's are known for having thin coating and replating is often needed. Once replated the stuff over here is good quality and you should not need to do it again any time soon unless you sieze a piston or other damage.
Niks Pro-X also makes piston kits for most bikes (inlcuding the KX65)/ We just put one in my sons KX with good results. I personally perfer the Pro-X since they are they appear to be the same size, quality, material (and often P/N) as OEM. I have been told that Pro-X manufactures many of the OEM pistons. I am not saying anything bad about Wiseco. I just like to stay as close to OEM as possible while saving a few bucks to let you know there is another option.