I like the Roll-offs, but they do have some disadvantages:
- The "system" costs more, so the initial investment is higher.
- Water under the film can be a problem, both with vision and with pulling the string to advance the film (film gets stuck to the lens)
- Every so often the little thingy on the end of the string pulls off and you're screwed. Replacement canisters are nearly $20.
- Have to put some duct tape over the latches where you open the cannisters, otherwise they'll break at some point (tree branches/leaves like to grab at the cannisters). Can't buy the canister covers separately anymore, so you end up having to buy a whole $20 cannister.
Despite this, I still like them better than tear-offs because the tear-offs get blurry if they aren't perfectly clean when installed (the more tear-offs, the worse it gets). And when water gets inbetween the tear-offs, you're screwed (there was some special tear-off lense that could be bought, along with special tear-offs, that was supposed to keep out water but it didn't work that well for me). At least with the roll-offs, you've got a fighting chance to advance the film a few times and get the water to work its way out. I do use the Smith "visor" things that stick on the lense. Contrary to what seems to be the intent of the visors, I run the tape on top of the visor, not undernearth. The visor (when used as intended) might keep out some water, but the film will still stick to the lense and make the advancement nearly impossible.
Also, at muddy races I will tape a tear-off over the roll-offs, so that if I get hit with a bunch of mud at the start, I can pull off the tear-off and then use the roll-offs from there on.