Malc/Marc,
If finances allow I would most definately opt for the Omnivac with the camera as an additional option.
However, if spending several thousands of pounds are out of your budget (like me) then the Norther Tools Gutter Lance system is most definately a good option.
Any debris is forced down the downpipe and collected at the bottom. You can then quickly blast the outside of the gutters themselves and finish with a window clean (with wfp) not the lance BTW
Its a fast, easy, effective alternative and once you have mastered the technique you wont need to check your work with or without a camera.
To date we have never had a customer ask for proof they are fully cleaned.
I have heard nothing but good reports about the Omnivac system though and Rods system above looks fab.
Sarah