Seems like there's not been much conversation about the Spiderjack here for a while. It's a shame, because (with a few months of practice) it is a fantastic, smooth tool for moving quickly around the canopy.
Spiderjackery HD
There are of course disadvantages, as it is in some ways a big change from a traditional or VT setup. Not being able to attach midline makes planning the climb more important, and removes some access possibilities... but adds a whole load of other ones. It is possible to footlock the doubled line above the spiderjack, and then tail the device up to meet you, just as if you had a groundie tailing a VT up from below.
The main difference for me, however, is not the smoothness or speed of the Spiderjack, or the distance it adds to the range of your jumps (after all, that's mainly just for fun!) but the massive reduction in the energy required to spend the day working around a large tree. It's so much easier on your body! I reckon this one device probably adds 5 years to your climbing life.
At first, until you get the hang of attenuating friction with the wooden block, your instinct (if you are used to a prussik) is to try and attenuate friction by actuating the cam. This gives the jerky, stop-start climbing that everyone complains of, and also wears out the cam scarily fast: I had to replace my first cam after just 5 weeks. After that though I started getting the hang of the block and the cam lifespan improved, until now I use no more than two a year, or maybe even less. At that rate the system is cheaper than prussiks - I used to go through a spliced prussik every few months.
Anyway, thanks for reading my 2 cents. If you've got the time, check out
my video , which demonstrates better than I can explain why I couldn't go back to using a hitch