They're super fun, actually. We figured out our old upright freezer was costing us like $80 a year in electricity - so sold it for $50 and replaced with a chest freezer that costs $15 a year instead.
Unfortunately I can't plug it into my milling machine or welding gear (darn 240v equipment!) and see how much power I use in the shop...
Sometimes libraries or county extension offices have them for loan, too, if you don't want to spend the $20.