Another good comparison! It's basically a cartridge bag. I love the Bobby but never bought it, the logo seemed too obvious for me to feel comfortable for everyday. Now I look at it, it doesn't seem that obvious, but it's a hard bag to just turnaround. The buckle fastenings are a really nice touch.
There is a Horsebit 1955 with the rounded bottom, it's closer to the Bobby/cartridge shape. I tried it along with the Small Horsebit. My friend I preferred the different shapes on me so I didn't get anything on that occasion. I still like my 25cm best. I can use the bag all day long, a smaller bag would mean carrying 2 bags.
I hear that they are discontinuing he Bobby(?)
Gucci seem to be only stocking the classic colours of the 25cm too. I wouldn't mind another classic bag like either. It's make yer mind up time for both of us.
If you can try the Bobby and the Horsebit 1955 on the same day, it's worth it.