With my previous Mk1, the recorded temperature readings weren't that far off from my Citizen Hyper Aqualand and my Shearwater Perdix. I actually have a lot of faith in the Citizen.
Here's an example from a recent dive with my old Mk1:

The Perdix is always slow to catch up, but once it does it is consistent.
Here's today's dive:

What is weird is the Mk1 never showed less than 15ºC and was on 16ºC for most of the dive.
Hopefully it is a one of and subsequent dives will show better results.