there definitely is a different feel when full, but it doesn’t bounce much; the bag holds it pretty well - also it is much more adjustable than a fuelbelt since it is one size fits all.
just make sure to evacuate all the air before putting the lid on - you do, however, have to re-tighten the belt every once in awhile as the bladder empties.
before I got this I used a 5k fuelbelt (2 bottles) and a REI waterbottle holder. The fuelbelt is ok, but only holds 16-20oz and I can’t see using the 4 bottle belt. The rei holder is very large and does move around too much.
got mine on steep&cheap a couple of months ago - just ordered another one when they came back up yesterday. $16