I was researching the same thing as my son needed a new car and hertz sales had some good deals. I saw a comment on another message board that pointed out that those who had actually experienced buying a previous rental car and had posted, usually had positive comments. Those who hadn't every purchased from a rental car company, were very strongly in the negative.
There weren't a lot who actually made a purchase and then posted about their regretful experience. If you have AAA, Hertz gives an additional $300 discount. My son ended up getting a certified pre-owned from a different dealer, but if you can get a late model that's still under warranty, I would consider it.