I've had my eye on that device from UK brewing as well. Currently I just struggle away with a screwdriver, knife, and hammer. It's not a pretty affair and it's the biggest single hassle in dealing with casks.
Having done a fair number of shive extractions at this point I'm pretty optimistic that the design of that thing would work. Though, you may be able to do the same for cheaper using some black pipe and fittings. I'm thinking a 1/2" pipe for the handle, reducing bushing, and then 1/4" pipe for the bit that goes through the shive hole. You could probably put that together for about half the price from local home depot parts. I'll give this a try when I do my next cask, which will probably be St. Paddy's day.
Any chance we could get you to put a quick camera phone video on YouTube showing your technique?