Why not enjoying that central triangle our bicycles give us?
The frame bag gives us a great extra capacity on our bike trips. Personally, I use it as if it were the drawer of forgotten socks, a mixture of tools, spare parts, medicine cabinet, cans of beer, Coca-Cola and pack of pasta for emergencies. In short, whatever I buy in the canteen and I don't know where to put it. What else would you carry in your frame bag?
You can order your frame bag with a waterproof zip or roll-top closing system. My advice… if you are one of those who are going to fill up the bag until a pin fits (like me) you can trust that with the roll-top you can do it without a problem.
It also depends on the type of bike you have, if the inner triangle of your frame is small, it may work better with a zipper. Ask us if you have any doubt!