I assume you are referring to the MTX Trunk DryBag. Pretty neat, but I prefer the looks and design of the EX bag, even if I need a rain cover for wet days. If I lived in a climate that saw a lot of rain, I'd consider Topeak's DryBag products.

One problem I have is that whenever something I've bought is updated and/or upgraded, I develop a bad case of bike/accessory envy.