I posed a similar question here not to long ago and got my answers, here is the link, you may find it helpfull.
I also did not like the tree strap but prefer using the rope with the prussic hitch as I climb and descend from my stand. I feel for me its easier to manuver up and down the tree and obviuosly just as safe.
As far as your straps getting loose on the leg portion of your harness the same has happened to me, but running it back through the buckle as you described should take care of it. What happened to me recently with my vest harness was after being up in the tree for a few hours I noticed something hanging from under the seat of my stand, what happened was that at some point either while I was walking to the tree or while climbing, the seat belt style button of the buckle got unsnapped and the strap from my right leg came undone altogether. What I do now is before I start to climb and once I reach hunting height I recheck those buckles to be sure they didn't get unfastened.
Hope this helps.