I've just made a couple of dives with Halo 3D and a Trilaminate drysuit.
The total time of each dive has been nearby 75 minutes in water always at 10° C (50 Fahrenheit degrees).
Notice tath I've been still and motionless for all the dive time because I've do team exercises...
I wear only a thermic T-Shirt and thermal protection was ok.
When the water will be colder (5° C / 41 F), I'll use a Xerotherm Base Layer under the Halo 3D and I'll sure that cold will not be a problem.
I'm very satisfied about flexibility...
Halo 3D provides more flexibilty than the neoprene drysuit (with a fleece undersuit) that I used so far (2 years).
In my first dive I've flooded my new drysuit: the dump valve has not been properly assembled and the right dry gloves have had a leakage...
Both my arms have been totally drenched, but I've not been cold.
It's the same thermal perception You could have with a good semidry suit... not very warm, but not so cold to drive You crazy...
The only thing I'm a bit disappointed at is that I need extra weight...
When I used a neoprene Drysuit I don't need lead when I use a double tank and steel backplate...
With Halo 3D and trilaminate drysuit I need about 5 kg of extra weight, and I was in FRESH water!!!