I like it. I think that's the Little Joe bag.
I just bought a similar sized seat bag. Mine is the biggest seat bag Jandd makes. Your Little Joe is wider and shallower. The Jandd is narrower and extends back farther. Capacity is about the same. Probably the Jandd is lighter and more aerodynamic. The Rivendale bag looks better and is probably more durable.
I think it is a good size for a change of clothes and a lunch.
Edit: The Jandd is cheaper too. Mostly because it's just nylon instead of waxed cotton duck.