Flip-flop hubs work great and don't cost much more than without. IMHO, the biggest problem with riding a fixie on hills is not climbing but going downhill. You can simply stand to climb most hills if necessary, but it is very hard to spin fast enough going down long or steep hills on a fixie without hitting the brakes a lot. My commute route has a lot of hills, and I had one of my bikes set up as a single-speed with flip-flop rear hub for a while. I ended up leaving it on the freewheel side because I didn't like having to ride the brakes on many of the hills. I've got a pretty good pedal stroke but spinning at 130+ rpm is a challenge for most cyclists. I eventually went back to having multi gears on that bike because the single-speed was doing a number on my knees.