I have been doing quite a bit of research on cam swaps since I have a pair of CompCams sitting in the garage waiting for install. Most people say that this tool is a waste of money. You might want to post over at Modular Depot or search thier old posts as quite a few guys over there have done cam swaps and they aren't on this board much. The only specialized tool I plan on using is the valve spring tool that is specifically made for the 4.6L
http://www.thetoolwarehouse.net/shop/OTC-7928.html
Here is a link to a good article about swapping cams. It deals with PI cams in 96-98 'Stangs, but would apply to other cam swaps as well. He doesn't mention the locking tool in his tool list either.
http://www.modulardepot.com/?show=articlesdet&aid=12