Wll, I haven't used these myself, but I looked at the specs on REI's web site and they look like a slightly junior version of the Ortlieb waterproof bags that I have. And those smaller ones are on sale for less than $100 a pair through Sunday!
As others can attest on this forum, REI has an outstanding return policy in the event you're not satisfied with the bags. Sounds like it's worth a try, they look great.
Ken