I have used both regular front and rear racks, and low-riders on the front extensively on very long bicycle tours. I have my set opinions, and I am not arguing against anyone else's opinions. Nor am I here to refute anyone. In my own opinion, low-riders are just some sort of fashion. Yes, they do lower the center of gravity. Of that fact there cannot be any question whatsoever. The thing is, I simply have never been able to discern any advantage whatsoever to having such a slight lowering of my center of gravity while on my velocipede or off of it. In addition, I could not mount a light on low-riders. Also, on my many small treks off of the road and into the thickets for a place to lie down and sleep for the night, the bottoms of the panniers kept being bumped by rocks and low plants. The fact of the matter is I gave away my last set of lightweight low-riders, and I have no intention of ever using another set of Cannondale low-rider racks I had stored away and forgotten about. I use front and rear racks, and they are regular, flat-top racks. They are pefectly fine for touring, and I have had no problems with them where functionality is the matter.
Low-riders are functional. They will hold you panniers. They will lower your center of gravity. I just have never seen any advantage with them. If there were a real, feelable, discernable advantage, I think I would use them, but I do not use them. On the other hand, some people with more bicycle touring experience than I have may be able to give you glowing and convincing information for using low-riders. I can only speak from whatever experiences I have had, and I am only one person. Use low-riders. I am sure you will never regret it or be sorry you did.