I've got one and it works ok for me. Obviously not waterproof but I don't intend to get it submerged in water. Most people tend to keep them in a belt pouch or little leather bag, both of which Help to keep out the damp.
Good thing about a brass tinder box like this is that you can strike sparks directly into the box (which can be useful in damper condition), get tinder smouldering then use it to catch light to your secondary tinder bundle, or light a candle etc. You can also, while you're at it, add a bit extra dry material into the smouldering tinder in the box. Shut the lid and it will extinguish your smouldering tinder but not before its charred the added material which means next time you come to use the box you have more charred material ready to take a spark. You can only char a little material at a time like this (not like making a tin full of char cloth) but you can do it in the go, making sure you've got enough charred material for next time. Normally used with a proper flint and steel for that traditional feel.
Good fun but still easier to use a ferrocenium rod - they produce a much hotter spark and will light a wider range of tinders directly without the need for a tinder box full of pre-charred material. The cooler spark from a flint and steel works better with charred material, hence the need for the dedicated tinder box.
