We have had bith Hot Gear and Transpack bags. We used to keep both our pairs of boots in the one HG bag but had to buy 2 Transpack bags to handle both pairs. Both brands have very rugged, well made bags. We had the HG bag for almost 10 years.
The issue with these bags is the heating element. Either the switches go bad or, more often, the heating element just fails. After 15 years with two brands I would say the heaters average 3 to 4 seasons of 30 to 45 days. The HG lasted a little longer but not much.
Getting the new heaters is a PITA. Transpack has an arrangement with
JenSkates for replacement heaters, but they won't sell you a new one until you have sent your old one back. That means that if your heater dies during the season, you are without one for 2 to 3 weeks. Presumably this is to prevent people from Gerry-rigging a non heater bag.
All a long prelude to asking of the Kulkea uses an improved element and what the experience of the long term owners has been.