I once fitted my Brompton with one of these carrying handles (the very original), but I found it a useless addition of 200 grams. However, one nice additional feature it had, was a shoulder strap you could attach to the edges of the handle. But then, I found that I could simply connect the shoulder strap under the saddle (Brooks) and the hinge in front , and it has been working just the same, no need for the stupid handle!
I must stress that holding the folded bike on one's side or back with a shoulder strap allows one to mingle with the crowd while boarding a train etc. And is much less offensive to everyone around than towing a folded bike in front or behind, and constantly lifting the thing and closing it again, when it hits some obstacle, and especially when in a hurry... With some exercise, securing the shoulder strap in place using the proper carabiners (such as Hero Clips), takes virtually no time, and requires no overhead during normal ride. (I've also heard that some people carry the folded bike in some sort of backpack, but I suspect the entire procedure of preparing the pack might be too time consuming).
For all I see from the pictures, I believe I will be able to do the same with my Helix (when it comes...)