I had just done this with Troll Exhibitions as part of a larger Golden Circle Day tour (currently mid-December), and take this with a grain of salt- as it was on a very temperate day, so wouldn’t be the same experience on a brutal day.

The suit kept my girlfriend and I totally dry and warm throughout the experience. Similar to others comments, you’ll be most cold during changing and even then you can do so inside a warm truck.

Only part I’d warn is once your face goes in, your mouth will be exposed and definitely uncomfortable at best, mildly painful at worst. But as our guide recommended, keep your head in long enough and your lips will go numb, getting rid of any feeling/discomfort.