I'm totally unimpressed with re-proofing using expensive Nikwax and stuff. It looks great just after the re-proof but it wears off within hours. I still do it every now and then but I'm disappointed every time.
I agree. Seems to work mostly OK on my Paramo stuff but not so great on my membrane-based waterproofs. Looks impressive doing the tap test but out on the hills, in fine blown rain, it wets out after a couple of hours.
I've said it before but I'll say it again - by far the best proofer I'm aware of is 303 Fabric Guard. That stuff is pretty much the same as the original PFC coatings you got on Goretex jackets in the past. However the reason they got rid of PFCs is because they're toxic to the environment and maybe even a little to the user. I think 303 is PFCs. I must admit to still using it.
If you do use it, you want to make sure your jacket is properly clean first - as in any Nikwax or other proofers removed. So you want to wash it in normal detergent, then Tech Wash (or liquid soap flakes) to remove the detergent and then a couple of rinses and then get it bone dry. Then you spray it with the 303.
My decade old Helly Hansen shell now beads like the day it was bought, possibly better in fact, and it doesn't just give up in fine mist, or where the arms rub etc, which I find Nikwax does. It's got that slippery feel to it that old DWC coatings used to have.