Yes the weight advantage does go up with the larger sizes. In the range of the BV450 and the Scout it is something like $190 more to save 5 ounces. To me that isn't worth it. I can still fairly easily get down to a 15 pound backpacking base weight even carrying a few extras. Of course the value in dollars of those 5 ounces of weight savings is a judgement call.

As far as larger sizes go... I can go 5 days backpacking with the BV450 by carrying the first day's food outside the canister so again I have not felt the need for bigger on solo trips. I do have a bigger canister (Garcia) that goes on family trips, but it gets carried by someone younger and fitter than me. I have decided that in general I am unwilling to carry more food than that any way. Most longer trips that I would do food drops can be arranged to keep the distance between restock at or below 5 days. If I ever do decide to do a trip that the BV450 isn't adequate I'll either bite the bullet and carry my old Garcia or rent a Bearicade.

For bike tours on roads, even dirt ones, I have never carried more food than would have fit in the BV450. In fact I typically buy frequently enough that I would never even half fill it on my typical tour, since I usually buy only enough to get to the next town with a store (plus a little extra just in case). I guess there could be an exception where I might, but I have never felt the need to carry one on tour. I can see where someone might carry a canister to avoid the hassle of hanging food, but I have usually found that the places where the problem is bad enough I tend to stay in parks that have bear (or raccoon) boxes.

If I owned one I might consider taking the Ursack on some of my tours, but I have not yet decided it made sense for me. If it was accepted for backpacking in Yosemite and SEKI I would probably own one.