I have the LaRue 9.0 now and I'm going to get the DD for my next build.
They're both fine, the only difference is that the LaRue will not loosen because of it's locking mechanism, but it's slightly heavier than the DD.
If you want the lighter feature the DD is a better choice.
Some of the members here said that they use blue Loctite on the DD threads so it will not get loose and said that it works.
Installation should be similar exept installation of the locking mechanism of the LaRue is just placing the bracket between the upper and the barrel nut before installation and finishing it by adding two machine screws with blue Loctite.
Try to see if some dealers like G&R Tactical or Global Tactical has them in stock.
I bought my LaRue directly from LaRue Tactical online because at the time I bought it, end of last year, nobody had them in stock.
I waited about four weeks before I received mine but they gave me a free LT cap and a armadillo shaped bottle opener.