Simplicity wins! It is easy to make something flashy, attach some bells and whistles and call it the next best thing. "If it ain't broke, don't fix it" trumps bells and whistles any day.
Most tail bags are a dime a dozen, and most of them pretty much do the same thing. However, the first thing you notice when opening RevPack's Seat Pack is the liner. The material looks similar to the inside of a lunch box. It may just be because it can be used as a lunch box/ice chest. It is recommend to use with a liner though as it may eventually seep.
The next best thing is that the bag has a lot of interior space; it boasts about 2,000 cubic inches of space. If you are counting, that is 50 cans of beer! In my case, that is five lenses with case, a DSLR, two mobile phones, and two water bottles with extra space left over.
I have to admit that their customer service policy is a bit crazy though. Of course they fix anything resulting in their error. However, if you go and screw something up they'll only charge you half the price.
Oh and if you ever managed to wreck into a lake, river, pond, or ocean you have nothing to worry about. Detach the Pack from your bike, it floats!
Warning: Do not use as a floatation device!