My experience with halflingers is limited but I have ridden several, all of which had rough upper gates; as many pony type breeds do.
I watched a video of an Amish horse show where they were mostly using halflingers. Some of those horses appeared to have nice smooth gates so I know that all halflingers are not rough. Also how rough a gate is on a horse is a pretty subjective thing, what's rough for me might not be rough for you.
I would not let the rough gate keep me from having this breed, I think they are super horses. An added bonus is that they are easy keepers.