This kit consists of four small blocks, four eyestraps for mounting them, self-tapping screws for mounting the eyestraps, two lengths of shock cord and four Sea-Dog shock cord hooks. By crossing under the tramp a few times you add a lot of length to the shock cord which gives you more stretch when you need it (like when you pitchpole).
The self-tapping screws supplied with the kit are not the way to go. Drilling and tapping would be much better; the cutting threads in these screws are too fat and too fine; they load up with aluminum and enlarge the hole, then the rest of the screw is loose. If you get everything exactly right they're OK as long as you can get the threads to bite immediately; otherwise the screw spins and too much metal is removed. The screws should at least have more taper and deeper cuts, if not coarser thread.
The eye straps are barely large enough to let the blocks move freely under the side rails. In fact, they don't move freely. This probably isn't a big deal since they should pretty much stay in one orientation forever, but it's just how it is
The Sea-Dog shock cord hooks included have small holes in them and you cannot conceal a stopper knot in the end.
The big thing, though, is the shock cord itself. Each section is 15' long and can stretch about 100%. Unstretched, it crosses the boat twice (shroud to block on opposite rail and back to the near rail). Installing it as intended (across the beam three times) already uses up about 50% of the stretch (it's very tight at that point), and in the event of a pitchpole there less than 10' of stretch left before you get to the end of it and break it. I would barely make it to the forestay before reaching the end.
The concept is great, but there's really nothing about the 14709 kit that was done well. You are much better off building your own system and using better hardware and enough shock cord to give you the most possible stretch.