I have two of the Kuhn Rikon spill stoppers. I love them. I also purchased the Kochblume ones this week. When you want to check the contents of the pot, all you have to do is slide the pot off of the stove eye for a few seconds and then lift the spill stopper to check inside and return the pot to the eye. I have a smooth top stove so I don't find this any trouble at all.
These are invaluable for me as I can turn my back on my boiling pasta or boiling potatoes and not worry about it boiling over.