The H series coatings are substantially more durable. The coatings themselves don't hurt the scope. It's the prep. Without proper prep neither is very durable at all. Be sure to mask off the power ring, threads or seams near the occular or AO assembly and anywhere else you don't want grit or acetone to get into the scope. Depends on the scope manufacturer to know if the warranty is affected. The reputable scope makers go on the nature of the defect and if the coating caused the malfunction and if the presence of the coating will affect the repair process. The H series gets harder the longer you cook it up to where it's fully cured. It needs a minimum of 250 degrees to set it fully. Any less and it will always be a little softer. Air cure gets harder over time but still never as hard as fully cured H series. Either series is going to be way better than any other sort of finish you can apply.