Just fitted a set of Jaws mirror extenders.
My mechanical skills are legendary but as you only need two Allen keys (one to remove the mirror head retaining bolts and a smaller size to replace the new bolts) and a Phillips headed screwdriver, even I managed to do it eventually. I took about an hour but I reckon a competent spanner-wielder would have it finished in twenty minutes.
Of course, it would have been a much quicker job if I had fitted them the right way around in the first place, but now they are on the bike they make quite a difference. As I am no longer as trim as a racing snake (porky bastid, according to the wife) I have always had a problem with my arms filling the mirror view but these extenders seem to have done the job.
My only criticisms are that thirty quid seems a bit steep for what is essentially two pieces of machined plastic and six bolts, and the 'fitting instructions' are more than a little vague. However it's been a worthwhile mod, all told.
Rob