I'm with Mike on the redundancy issue and I prefer to use a slung 30 cu ft deco bottle. You can hand it out of the hole at the end of the dive so it adds no weight when you climb out of the hole. In my opinion, most agencies are overly bound by tradition when it comes to ice diving and are well behind the times compared to other technical/overhead/penetration activities such as wreck diving and cave diving.
I also agree that a good cold water reg should not pose any freeflow issues, particularly if you use good cold water techniques, such as not inflating the dry suit and inhaling at the same time, not testing the reg before the first stage is fully submerged, not inflating the BC/wing prior to the dive, or anything else that increases the cooling of the regulator. Locally divers have a lot of success with the SP Mk 16 and SP Mk 2, but my personal favorite for cold water is the realtively new Mk 17. It's as bullet proof as you can get and most SP second stages alos do very well in cold water, particularly the G250 and X650.
With any regulator, it often helps to remove the rubber hose protectors, or at least slide them back off the metal LP port fittings as this then allows more heat transfer from the first stage. Removing the rubber trim boot/protector found on Scubapro second stages and other brands over the second stage LP inlet fitting can go a long way toward improving the cold water performance of the second stage as it is one of the few direct metal to water parts on the second stage.
Ice diving is do-able in a 7mm wetsuit, but you will want a warm day and a warming hut of some type. With a drysuit, it actually becomes enjoyable.
Ice diving is by nature a group activity and with 3-5 people, the work load per person is fairly small. Visibility under the ice can often be superb in lakes where it is only mediocre when the water is open. But, select buddies carefully, because one moron bouncing off the bottom or finning the silt up will permanently screw the visibility and it's a lot of work to move the dive site. Technically oriented divers used to overhead environments and with excellent nouyancy and finning techniques are an asset. In any event, discuss it up front and put the new or more silt prone divers at the back of the rotation (and still supportively voice the expectation that they do the dive in a silt free manner.)
Techniques also seem to vary slightly by certification agency and location. When I orignially certified, lines were fixed in the ice with ice screws and the protocol was one diver in the water and one safety diver on the edge of the hole with a longer line. Locally, the tender holding the line is the only security for the line and they put two divers in the water together (the buddy system).
Tended lines tend to be short on the premise that you need to be close to the hole in the event of a freeflow, etc and I think that severely limits the fun of ice diving. Personally, I like to use wreck penetration techniques and run a reel from a down line, but it's minority view so I seldom get to use that approach.
One thing I often do early and late in the year when bays are frozen over but the lakes are still open out on the points. is to enter open water and then set a line and "penetrate" back under the ice shelf. With adequate redundancy have much more freedom of movement with no compromise in safety. And if you can follow a compass course, you can recover from a lost or broken line just by following the bearign back to open water. So if you are advanced wreck or cave trained, it may give you another option for early and late season ice diving.
Kinda like flying a helicopter as compared to a cessna
