For the first few years after getting the OW cert, I took maybe one dive vacation a year, using rental gear from whatever dive operator I was diving with, before finally ponying up the money to buy my own. Some of that rental gear had seen a lot of wear, but all of it was in working order. If a rental reg was difficult to breathe, then I told the divemaster and got a different one the next day. A thousand bucks for a set of gear was (and still is) a lot of money to me, and I wasn't sure I was going to be diving that much. As it turned out, for the first few years I did not in fact dive that much. So in retrospect I believe holding off on buying a full set of gear was a good decision for me. I think the quality/safety of rental gear is generally fine, and the decision whether you should buy or rent should depend mainly on whether you fall in love with diving and how often you go diving. Sometimes it's not apparent at the time one gets certified, because at the time we finish the cert course most of us are all gung-ho about diving and tell ourselves we plan to do a lot of it. As the months go on, and things get in the way of our plans, we find the reality may differ. All of us have different situations.