agree with the practice part, and IMO not all climbers are created equal when it comes to how sturdy they feel in the tree. If your current climber doesn't feel sturdy then I would borrow/try others till I found one I like.
Also, check out third hand archery stabilizer straps. I would add those to any climber; with those you have the confidence that your bottom cant slide down will climbing and once in position and pulled tight your top wont get bumped and drop.