I had thought about heated clothing some years ago, there were heated jackets and pants marketed for motorcycle use. But with my older sleds, there is not enough watts output for them. Newer sleds probably have enough though. Something to check before you make a purchase.
Those were 12 volt external source supplied. I suppose the Milwaukee jackets are used with a battery.
Something to think about when using them is if they fail. When using heated clothing, you may not have as much other clothes on as you would without it. If there is failure that caused them to lose the heating a long way from home on a cold day, it would be a bad thing. I always keep some warm packs on the sled for times they may be needed and keeping several along when using the heated clothes would be good for backup.