Hi Wooly
Its really worth doing. My 110 has gone from a top speed of around 60mph to around 80mph. Certainly makes cruising along much more relaxing.
Ashcrofts did mine for me + put in recon ed G + T boxes (didn't need them, but thought it would be a good idea at the time.
Once you've done this, remove the cat (if it has one), centre box and blank-off the egr.
If you have any cash left after that, get your vehicle to Porny or BAS (if you haven't already).
Fuel consumption for me is much improved - 30mpg on the dot now.
Tom