I raced a jet 14 as a teenager a long, long, time ago. Then they were molded plywood built by Sidnons and Sindle in New Jersey. It was a period International 14 hull with a Snipe rig. It had a steel centerboard. They were an active two person racing class. They would plane and had a rig that teenagers could handle. The big jib for the time made them speedy. The lines were the same as a Thistle but in a smaller boat. At the time builders could build different freeboards. So higher sided boats were in rougher waters while lower boats were for calmer waters and all out racers. A big improvement was going from a wood mast to aluminum. Tied up in a slip if the centerboard wasn't down the boat could roll over if there was a lot of wind and was wave action. I great liely boat to sail without being hard to handle, but not a family daysailer.
The Jet 14 is a excellent lake boat. I bought mine back when I lived in NJ since there was an active racing fleet on the reservoir nearby. We raced the boat constantly for about 10 years. The last poster has all the details right as far as the linage. I like to describe the Jet as a little big boat. It has a main, jib and spinnaker so you got all the parts if you want to play with them. The boat is responsive and quick but certainly not extreme. The fiberglass boats are all tanked to they handle a capsize well if it happens (3 times in 10+ years). Hope that helps. Let me know if you have any specific questions.
As others have said, the Jet was essentially a state of the art International 14 when they were designed. I've only sailed a Jet a few times when I was on the sailing team in college at away events at a school with Jets. I recall that I really liked them. They seemed more responsive compared to the FJ's we has been sailing. The cockpit was more conveniently laid out, and the responded to tweaking quite nicely. They were less stable than the FJ's, They are not very tolerant of weight. If you put too much crew weight aboard they get much slower which we were told is why FJ's were more popular on he college circuit.
My first sailboat was a Jet 14. Plywood hull and a wood mast. Was living in northern NJ at the time (early 1970s). Paid all of $275 with a trailer. Fixed a few minor issues and used it for a couple of years then sold it for $300. It was a great boat to learn how to sail on.