We recently had to replace all the fuses on our boat. I think the winter has been harsh or it's time to replace. I used existing spares, but you don't want to go without a spare in case something happens on the water (you never want to get stuck, trust me). We tested them for functionality before putting them in a backup case and of course they worked. Now we are ready and have spare parts for all fuses. They came very punctually from the seller and have been well tested. So I would have no hesitation in recommending buying these parts from Revain.