I have been looking at clamp guides for routing and circ. saws, at about
50" long. The ones I have seen are

Trend CGS.
Dakota (from Rutlands).
Axminster ProGrip (seems pretty similar to the Dakota).
Axminster Perform.

The trend is most expensive and has accessories available etc (around
£45). The Dakota is around half the price and has accessories available.
The Axminster is around the same price as the Dakota but no accessories.
The Perform clamps are half the price for a pair, no accessories.

Has anyone used any of these or have any other advice on the subject?

Thanks in advance,

Alex.