Easy to access. If you have Ortlieb Atrack backpack, don't forget to get one.
Hooks up nicely. It is a bit tricky to put in, but I’m sure it will become easier with time. It is nice to have a cooler bag to keep the drink cold.
Fit perfectly into my 45L pack and should fit the 35 and 25. Haven't had a chance to use it yet, but so far looks like it will work.