Although you may have the winter tires on for a shorter period of time than the summer tires(although in my state it could almost be 50/50
) I personally would rather have the TPMS on the winter set vs summer set for a couple of reasons. One, in cold winter you tend to lose air more than hot summers and two, it's more a PIA to check tire pressures the manual way when it's single digits or below zero, it sucks!
This is my first winter driving with real snow tires(Michelin X-ICE3) and it's worlds better than the previous A/S tires I've used, my Leaf went from a fair ice/snow vehicle(the worst of the vehicles I have) to the best. Personally I'm just going to pony up the money to swap the tires off the rims twice/year. While more expensive now, my next set of snows will be purchased at Costco where they offer a $40 all 4 tires swap/balance special, cheaper than anywhere else I found including the $60 I was quoted where I purchased my current snows.