Your FEL will stop you if you back uphill; but won't do much driving up.
I have a Kubota B3030 which is also HST and my lot has very long, steep slopes. I am handicapped, so I don't have quite as much leg strength as most of you. I believe the comment about brakes having more stopping force going forward vice reverse may be true; I'm sure you've seen that in a car. It just feels safer backing up the hill. Also, I have a tooth bar on my FEL but, even if it's not on, putting the bucket down, either just digging in the bottom or all the way over like when I have the BH installed, pretty much keeps mine from going down my very steep hill. Add the extra stopping force going forward, and I don't have a problem. Digging stumps while on the BH attachment facing rearward is also less unnerving, and if it rolled I'd probably be dead.