In topic, I have the whole keis setup (jacket, trousers, gloves), my thoughts below.
I ride all year round, mostly a daily 70 mile round trip on motorways, plus longer trips around the country for meetings etc. Average annual mileage is around 15k in all weathers unless ice and snow are forecast.
The jacket is by far the most useful bit of bike clothing i own for the winter, it’s warm enough that even down to 0 degrees I don’t use it at more than the medium setting, and off the bike it just looks like any other softshell. It fits fine under all the jackets I’ve owned, and it’s wired to distribute power all the other so you just plug the jacket into the bike and everything else into the jacket. Good between 10 degrees and 0 degrees for rides of any length.
The trousers aren’t as useful, they only really come in when it’s properly cold, and/or long rides on motorways where the wind chill is greater. They’re designed like a very thin set of sweatpants and go under the existing bike trousers. The heating elements are only on the front of the trousers, (so top of the thighs) where the wind would hit you, not at the back, control is via a “tongue” that sits above the belt line and flops under the line of the jacket, so you can control the trousers and jacket separately. Power can come from the bike directly, but best plugged into the jacket. The low power setting is all you need in any weather above 0.
The gloves are decent, basically a goretex leather spring / autumn glove with a heating element across the tops and fingers. Surprisingly they don’t have any heating in the palms so you need heated grips as well. Sometimes it’s a faff getting them on under or over the sleeves of a bike jacket as the cuffs are pretty chunky, but it gets easier over time. They can be powered off the bike via leads run under a jacket, or plugged into the heated jacket (the best way) or you can buy small battery packs that fit into the oversized cuffs. Control is via buttons on the tops of the gloves. If you have hand guards on the bike you don’t really need these until the temps drop below 5 degrees, if you don’t have hand guards to help with the wind chill they come into play much earlier in the winter.
To me, the only downside to keis system are the controllers. Wearing the full suit you end up with a bunch of controllers down by your left trouser pocket, and though you can work them while riding with some practice it would be nice to have an option to put a controller (wired or wireless) on the handlebars like the gerbing system.
My advice to anyone would be to buy the jacket first - a warm core is essential on many levels - then buy the other components as needed.
Also, investigate putting as many deflectors as you can and a large screen on the bike for winter riding, as reducing wind chill means less heating is needed, which means a smaller load on the bike’s alternator, which helps with reliability.
