I use my horizontal zip cabas pretty much daily and I love it. I'm not sure it would make the most perfect travel bag, though, because even though it is huge, there is no way of closing it, so you have to be careful that nothing falls out of it if you're stowing it under seats or whatever. That said, I used it as carry-on baggage on a few flights and didn't have a problem with it - just had to be careful that things didn't fall out of it when I put it under the seat in front of me or put it in the overhead compartments. If you don't want that fuss then maybe a different bag would be better, but if it's not a problem then I highly recommend the bag! I haven't been precious with mine (I kick it under my desk at work, use it to carry all sorts of hefty things, etc) but except for the softening of the leather it still looks brand new despite being about 3 months old now.
I agree with sweetarrow in that it could do with a base at the bottom (I had the same problem with my DSLR pushing it out of shape) but it's not 100% necessary (I still haven't gotten around to getting one!) and it's still a pretty sturdy bag.