Fits anywhere: under the seat of a modern sportbike, behind the headlights, inside a Roadcrafter's oft-forgotten thigh pocket, behind your license plate, inside the fairing. No matter what you ride, you have room for one.
Holds heavy loads. Even after five years of occasional use, my old one hadn't torn or popped a thread or do anything but gain a fine layer of road grime.
Straps securely. Pull the straps over your shoulders, cinch them down and not only does that close the bag tightly (the heavier the contents, the tighter it gets), but pulls it tightly to your back, too.
Doesn't flap around. You'd think a bag like this would fly around wildly at high speed. But, because you pull it on tightly, it holds securely.
There are going to be things that won't fit. You'll be limited to 12 beers, not 24. A large bouquet of flowers is probably a bad idea, go for the small, friendship bouquet.
And some stuff is too small. A bottle of wine? We'd keep that to low speeds only. The bag just doesn't get secure enough to avoid small stuff flying about a bit.
Your friends will steal it. Invariably, you'll loan it to one of them in a fit of camaraderie as they try and take home a spur-of-the-moment purchase. You'll never see it again, unless you look under their seat.
An essential item for any motorcyclist, you'll find uses for it you never knew you had. It will make your life easier and more convenient and more spontaneous. Not bad for $25. Heck, get two.