Interesting how you have worded it. A lot of London controllers don't like CPDLC but logging on is not going to hamper their day, the ones that don't like it will just simply not use it. So no harm in logging on.
There are a lot of limitations placed on controllers when using it so most don't bother. Such as:
We're not allowed to use it below FL195.
We're not allowed to transfer aircraft on a heading using CPDLC unless it is to another London Area sector.
We're not allowed to give route instructions with multiple way points if one or more of those points has a three letter designator.
Also if you are a FANS equipped aircraft and the message times out, there is a big spiel we have to give the pilot about disregarding the message and disconnecting from CPDLC. So no controllers bother with FANS aircraft. ATN doesn't have this problem and so you're more likely to get controllers using it, however, there is also the time lag involved with aircraft acting upon any message sent which more or less rules out any tactical use of it (i.e. heading/level/speed instructions).
It is useful for finding out an aircraft's requested FL and to check for stuck mics however, so I would still use it if I were you. Maybe one day it will become more common place.