I just spent a year looking at various FELs and looked at name brands including the factory New Holland (7308), Woods, Great Bend and Bush Hog. None of the ones I looked at had only a single hydraulic cylinder on the bucket. So, there must be an advantage to have 2 or so many manufacturers wouldn't use 2.
As for staying with the same brand as the tractor, most do, but there are quite a few folks that have non-factory brand loaders and are very happy with them. I just ordered a Bush Hog for my New Holland tractor. The Bush Hog has a higher reach, higher lift capacity, Quick Attach mount (and 1 less bracket to get in the way than the 7308 loader which has one going from the mid part of the tractor to the front on each side), matching color, and I'm getting the Skid Steer compatible Quick Attach bucket for less than a New Holland FEL would have been without the Quick Attach bucket. If you do decide to get a factory brand FEL, get it when you buy the tractor, since they are much more expensive to add on later. Non factory brand FELs are much cheaper to add on later.