Nicky:

I find the metric system to be significantly easier – I’ll never go back. I do have to work in both, though, purchased plans, or someone else’s specs, are inevitably in Imperial. One thing with metric, is that you’re always working at 1/25th of an inch (if the inch is the standard) – the scale of my ‘acceptable’ tolerances just improved (certainly, you could say the same for working at a 1/16th, as well). Also, going to a set of digital calipers, and rigorously using them, made a significant difference – suddenly, I was able to fine-tune cabinet/case work.
Regarding the Wonderfence, I have the 17", and cannot see the benefit of the 25" (just me speaking). I use my RT a lot, and have never needed the 17" capacity, let alone a 25".
Incra is a purchase once system.
MJCD