I have been using it with my M8 and Noctilux, and while this hardly constitutes a comprehensive test, I've had no hint of a problem. Furthermore, the Y-strap inventor has this to say on his site:Looks pretty cool . Not sure i would use it other than a small sensor camera or M8 though. I do agree with Robert how much can that one lug handle. I know there strong but makes you wonder
I have spoken to many camera makers and each has indicated that there is no issue carrying the weight of a camera with lens from one strap lug. I had a conversation with Leica USA and they indicated that since the M6 (20+ years ago) all strap lugs are steel with two steel screws to hold the lug straight with no lateral movement.
Now I obviously can't vouch for warranty questions, but I sincerely doubt that using this device will cause an M8 lug to break off.