I have both the Troy Delta and a DD Omega. Both mount around and to the barrel nut.
The Omega is held in place by 4 set screws that press against the face of the barrel nut and by the upper and lower halves of the handguard. It is solid enough for rough use IMHO and I have never had one work loose.
http://www.weaponevolution.com/forum...ctorial-review
The Troy uses two plates that rest on top of the barrel with threaded holes in them that wedge themselves under the barrel nut and barrel. You position them so that the holes are roughly the 2 - 4 and 8 -10 o'clock positions. The handguard halves goes over the barrel nut and screws go through the handguard halves into these plates. The Troy contacts more surface area than the Omega but it actually comes in contact with the barrel. Granted it is immediately infront of the barrel nut and should not impart much in the way of flex into the barrel. The Omega only comes into contact with the barrel nut.
https://www.m4carbine.net/showthread.php?p=1550834
I think the Troy is a more sturdy way to do this but both are a compromise for not having to cut the Delta Ring and spring off your rifle.
I am having a difficult time getting use to it the longer I have the Troy. The tubular shape just is not for me. I am going to sell it to fund a CASV which I have used in the past and really like.