Just how big a difference do slippery lines make?
-normous but the question here is whether or not silicone (and anything else)
can return slipperiness to lines once time and use has diminished them. The answer to that is yes, but with caveats. It won't return them to pristine, box fresh condition and it won't repair actual damage, such as frayed lines. It's a worthwhile bit of maintenance though.
I haven't noticed much difference between brands but then it's not as if I've tried all of them in blind trials.
Without very slippery lines stunt kiting would be nowhere near where it is today and would quite possibly not exist in anything like the form it does.