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My buddy's got a Vanquish. My Atomics are nothing like an Aston Martin ....
In South Fla they are all over, but I move every few years for work and am based in Charleston, SC where no Atomics dealers are.
I like the Apeks' breathing a little better, but the Legend's ACD offers a little peace of mind; I'd recommend the Legend LX for value, features, serviceability and performance.
You point is very valid.
An additional factor involved in my case is inattentiveness ( I was not intended to be the primary user... ) . Given the likelihoods of failure due to water entry vs. spring failure / check ball disintegration, the choice was the " lesser evil ". If the ACD ball & spring is easily removable - might that erase its' demerit ?
I don't see the ACD being a major failure point simply due to the geometry involved. I highly doubt that it could fail in the water since it would have to push the yoke away from the first stage. If it fails on the surface, then its an annoying repair but not life threatening.
I think its a lot like heated seats in a car though. It's a nice feature to to have but isn't a must. It's just an exapmle of a plus for this one and a different plus for that one.