Didn't Michele use her Platys for hot water bottles on the AT? I think she had problems eventually but never anything catastrophic.
I have used a hard Nalgene with no problem but a knock-off leaked at the cap. Solved that in the short term with a small piece of saran wrap over the threads before putting the cap on. Solved it in the long term by introducing the knock-off to the trash can.
My son had a regular, rubber hot water bottle spring a leak this past week but it did have several years of almost nightly use during the winter on it so you really can't complain. They regulate the heat pretty well but are too heavy for hiking. I just don't appreciate the hardness of a Nalgene, even stuffed inside a sock.