Why do you want to use them over fixed blades? If it's because they fly better then you have some problems that should be fixed. If a fixed blade flies like a laser out of you setup all is right, if it doesn't even a mechanical will be carrying alot of baggage. Sorry if I'm preaching to the choir here but I can't see any reason to use them unless you can get good ones for free, (even then maybe not) or an outfitter requires it.