I have an older version of the Jig-It Hinge Mortising Jig (from around 2008?), this is the only article that I can find on it so far. Although it can only be used to cut the mortise for a butt hinge, it is adjustable for fairly wide range of sizes - a little hard to see in the photo, but the wood stop can be adjusted in and out to give the width of the mortise, and the aluminum base can be adjusted to suit the length of the hinge - it does that very well, with only two adjustments. Ways to Cut a Hinge Mortise / Rockler How-to
Here are a couple of photos of the jig in use - I was cutting a 3/4" wide notch in the sides of a cabinet door for a retainer strip to keep stuff falling off the door when it was opened. I had to reconfigure the jig to get the narrow opening I needed but this gives the basics - a nice solid jig that works very well.
The jig shown in FWW can be brought to the next level by making it so it will cut the mortise in both parts at the same time. I made mine by gluing together strips of the correct width, but if you take two of the jigs shown and join them with a strip that projects below the face to be mortised, you can clamp the box and lid together with the jig "flange" sandwiched between them and both parts routed at the same operation - if you have two jigs sets, you can rout both at the same time and be assured that the mortises in both parts line up. I haven't seen that jig in a while, but will see if I can still find it.