I have an F-stop Tilopa and LOVE it. It's perfect in every aspect!
It's durable, it fits a lot of stuff, but you can tie it down when you don't need the extra size. I have a Shallow Small ICU and a Medium Pro ICU. A ton of gear fits in there if I use both. My favorite combination is the Medium ICU with clothes etc. It fits everything I would need for a weekend:
- Enough photogear
- Fresh underwear/socks for 3 days
- 2 shirts
- Hoodie/pullover for when it get's cold
- Extra pair of shoes/flip flop
- A book
- Laptop
- Chargers, filters, batteries, cables and misc. stuff.
- A bottle
What more can you ask for? You can always use gatekeepers to add extra stuff like sleeping bag/tent/sleeping mat.
I HIGHLY recommend them. They're a little more expensive, but totally worth it. Their guarantees are great too!