When I was young (40 years ago) I made two dives in an alpin lake under 80cm of ice
I was using a Technisub full face mask and a Scubapro Mark V (MK5+109).
Water temp. was +3 centigrade degrees, air temperature was around -5.
No icing, no free flow.
I did breath through the reg and the FFM for approximately one minute before splashing, for checking that the wired intercom was working properly.
I think that these solid brass second stages, and piston first stages with SPEC, were the best for avoiding problems in cold water.
At the time no BCD was used for these short dives at shallow depth. Hence I was weighted light, I remember I was very streamlined and perfectly neutral in my Rubatex wet suit (no external fabric layer over the neoprene, minimizing water friction).