If it’s the correct size, and the holder is in good shape (no corrosion, etc.) then I wouldn’t worry too much about it. Also probably not worth converting to a breaker- the fuse does what it’s supposed to do, and in the case that you’re on the boat to reset the breaker if it trips, you’re also there to manually turn on the bilge pump. So switching to a breaker offers little benefit.Not a glass tube and only 5amp. I think it is too small, but I'll cough up to fluke as it took 4 years to blow. Just performed normally on today's outing.
For what it’s worth, I’ve switched entirely to EasyID ATC fuses from Blue Sea Systems. They have a small LED in them that illuminates if the fuse blows. Makes it very easy to identify a blown fuse. They’re maybe a dollar more per fuse, but that equates to MAYBE $20 per boat, and in a good electrical system, they should never really blow. Well worth the money when it comes to quickly troubleshooting an issue. I use them on my boat and install them on all my customers’ systems.