I noticed for both the spindle and the smelter (and probably a few other tools, too) that it doesn't tell me how much energy I'll be spending to throw in x number of whatever. I know it refuses to work if you don't have enough energy to complete the task, but sometimes I end up with a distressingly low amount of energy and I just wish I could've been forewarned how much energy I was going to be losing.
(Additionally, it would also be nice if these tools could display how much of the product you'd be getting...)