Originally Posted by
JohnJ80
To be clear, there is no requirement to use two GT18's. They can be used individually. Unless I'm not understanding what you are saying.
True, there's no such requirement. What I mean by "form factor" is that two Ortlieb FRs are big enough for me together and yet can be used separately - when I need them both, I can put them on both sides of the bike for load balancing, or when my wife and I go out cycling, we both can use one. Yes, I could do the same with two GT-18s, but that would be (1) too big and (2) too expensive for me. If you check the prices of the two products, you'll notice that two GT-18s is twice as expensive as two Ortlieb FRs.