A number of interesting points raised - thanks all.
Justin: I played with the Manfrotto 410 in a camera shop on Saturday. I am not really convinced the adjustment is fine enough for what I want. Basically it appears to be designed to position cameras over angle ranges of 90 degrees plus and the knobs are a bit stiff for very fine adjustment at the one minute of arc level. It also rather expensive. I am making slow progress with a home built version .
Pete R: I will be checking the Bosch calibration against my steel tape, in fact they suggest setting up a fixed test range to check the laser on at regular intervals. Incidentally, steel tapes also rely on the manufacturer's certification unless we get them checked at a national measurement bureau which we never normally bother with. Steel tape inter comparisons which I have done invariably show them to be within spec.
Guido Bros: Measurements 50 miles from home are one of the occasions I want to use the laser measurer. I had some last winter in cold and frost and needed on the spot calibration. I no longer feel up to scrabbling around on the ground in such conditions, but I accept the solo method is really excellent if you can do this. I always teach it to new measurers.
Duane: I agree that short scale dips and humps would make course unsuitable for measurement by laser. But If the for example there is a single change of slope then the dip or bump can be measured relative to the laser beam and a geometric correction applied. One metre off in 100 metres amounts to a correction of only 5mm.
My other application is to lay out calibration courses on off road surfaces. We have been getting some queries from races on non-road surfaces who want road race certificates of course accuracy. We are planning to investigate the change of bike cal constant on one such course.