Hi Rob,
I've been using one this season when out for long days.
I got it for chucking a couple of boxes of salmon or pike flies in when travelling light. The pack/rucksack thing I normally wear encourages taking too much rubbish with me.
Trouble is, I have also bought a lovely goretex wading jacket from a certain scandi company and it takes a couple of boxes just perfectly as well.
As for kneeling down unhooking fish, I will have you know that my run of blanks is about to end in a spectacular style! I predict a double figure brown or a 30+ salmon!! lol