I'm a long time Thermic heated footbed user but the wires break and get annoying to have hanging around on spring days, so I decided to try the Sidas SET socks when I got some sock batteries on a mistake sale ($25 for a pair for the 1400B). I've previously tried the Hotronic XLP 2P and they were too thick.
The Sidas SET fit just like my ultralight socks in the toes, where is where I need the volume. Obviously the heating element does introduce some volume that a standard sock doesn't have, but it didn't bother me at all. Heating performance wise, I can't provide a good comparison since it was a warm day that didn't really call for heated socks, but my initial impression is that the socks provide more heat than the footbeds. Plus the form factor and fiddle factor is reduced.
Of course my ZipFits are already setup for heated footbeds so they aren't going anywhere, but if I had to do it all over, I'd go the heated sock route with these Sidas SET socks.