Honestly, when I got my Fathom I insisted on an ADV because I was so used to having one. However, as I said, I pulled the ADV out of my unit after a friend had a failure with the same ADV on her X-CCR (and since then I know another person that had the same failure on the X, and rddvet's wife had the same failure on her Fathom). Even without the ADV I still have two ways to add gas (MAV and BOV) and I found that this works fine, even on hot drop dives where I'm descending at 100' per minute - like I'll be doing this weekend (again) in SoFla.
I have to agree with @kensuf I hate ADVs but maybe I just haven't found the perfect one. I found the ADV on the rEvo sucked (apparently it's better now) so I turned it off and the SF2 one was super annoying if you were heads-up on surface so I kept it permanently isolated. I only ever used the SF2 ADV in class. The Defender I just bought doesn't have an ADV which suits me perfect.
My friends who are on X-CCRs have not had an issue with theirs as of yet but it is actually one of the questions that I first asked them.
I just hammer on my dil MAV all the way down for a hot drop. Even pointing a scooter straight down on the trigger I've never felt I had an issue adding gas to my loop. I have not really used an ADV in 6 years and am personally happy without one. One less failure point / potential leak for me.