Tim, I always thought the surge brakes where adequate, and convenient.
I converted our Hi-Lo to electric brakes (yes it meant changing the axles), principally because I was finally having such a difficult time procuring needed spare parts, and just keeping the brakes working. Two different Hi-Lo dealers had their way with the brake system, and neither was successful. So I made the switch and haven't looked back.
Incidentally, I never had problems with the brakes actuating when going downhill (unless I applied the car brakes). A good strong damper piston will prevent that. In hindsight, I do wish I'd tried a repair one more time...at a boat trailer specialist. That seems to be where the expertise is now
Jim