I have one. I will say that some bladders fit better than others. I have a 2l camelback, but it’s kinda long so it doesn’t fit perfect, but it works.
I could see using some sort of protection for the bladder, but there is no need for anything to hold a bladder.
As far as weight, 2l is only 2.2lbs. Not very much weight up top really. I was wondering how it would work if the lid was pulled down tight so it wouldn’t move around with a fairly empty pack. It worked fine.
I have been hiking with mine the last week and I think it’s a good thing. I plan to keep my day stuff in the pouch right below the bladder.
I’ll try to get a picture of mine tomorrow.