You’re not dumb, kbin isn’t as big of an instance as Lemmy or Mastodon so kbin would be in the “other similar platforms” category. If you like you can imagine the kbin logo and a green plus sign in-front of the Lemmy logo. It is of note that on kbin the “boost” is the true upvote button. The upvote button does show popularity but it won’t “boost” the posts to the front page.
Electrically comparable only if they are volumetrically, which they are not. Typical mini fridges have an average volume of 2.5 to 3 cubic feet. So approximately one sixth the volume for half the electrical consumption is not a worth trade.