I did not realize HSA could be rolled over. I am an employee and my place of employment offers an HSA thru AFLAC, but I remember the AFLAC rep stressing that it was a use it or lost it deal.
The 'cafeteria plans', IMO, are a bit of a joke, specifically because of the 'use it or lose it' clause, which forces people to waste money or buy stuff they don't need.
I did have one HR person tell me once that they'd cut you a check back for the diff if it wasn't spent, but then it counts as 'taxable income' and this was said with some degree of gravity, as if that was some type of 'ultimate sin' - having taxable income! I'd rather keep the 70% of my money rather than spending it on something vaguely 'medical' that I do not need, thank you.
One big advantage of HSAs is that if you lose your job the HSA money is still there to draw on if you need it.