I have several Ken Tool spoons. I recently purchased a pair with the little nipple that hooks on the rim however I have not used them to date. The curved ones seem to work better for reaching inside and catching the tire bead to remove, especially the second bead. The straight ones seem to work okay for installation. If you poke around the Ken Tools site there are some videos on how to use the tools which was helful to me. Overall I find there are all kinds of tire spoons and very little information as to just what is best for which.
The best money I spent was on the hammer tool (works like a fence post driver) to break the bead.