In reply to David Barratt:
Baron Weasel, when the Nikwax rep told you that he was referring (by mistake or on purpose) to reproofing coats and other garments which have an original DWR. Using heat on these garments reactivates any of the original DWR still present. Nikwax DOES NOT require any heat to activate it, however grangers products do. So in short you can only use grangers on garments which can be heated in a tumble dryer or over radiator, where nikwax is suitable for any garment or product even including jeans etc.
Have used rope proof in the past and would agree that it is nowhere near as good as buying a dry treated rope, but its use does have some merit.