Nice suggestion, thanks, Pete but, although I can live with the extra cost, the laser version has had good press. I had a SIP site saw with a laser and it was pretty naff. However, I just dragged the saw out of its' box (to discover more broken bits) to have a quick look at the laser line and it is very good. Thin, sharp and straight and so well worth the wait.
This is my frustration. I have been looking for a good quick way to cut lots of tenons and this was the best solution that I could come up with.