create the hole for the box. Recently I have seen these Box Sinker Sets
that
fit to an SDS drill to create a perfect hole and they also are used to
channel the wall out for the cable, has anyone any experience of using
these? If so, are they worth the investment? (not just for one job), or
has
anyone got any other tips for me to make the job easier and neater.

They are not worth the money for 1 hole and if your wall is brieze block or
cinder block the box sinker will rip the wall apart.

Focus do a frame that you screw to the wall. It has about 30 holes in it
that you drill through. When you unscrew it from the wall you get the right
size & shape hole. You'll need to use a bolster a bit but I find it much
easier to use than a box sinker and much cheaper.