I have never made my own box joint template, but I do have the Leigh Dovetail jig, and I bought the box joint attachment. I am very happy with the Leigh jig, but they are a little expensive. If you only plan to do box joints I think the jig you are looking at should work fine. If you do decide to make your own jig, I think it would be easier to make a jig for the table saw rather than a router.
