Just fitted my 591 rack to aero bars but used the clamp which is supposed to be used for the square bars. it feels solid enough, will it be sufficient? Has anyone done this or do i need to refit using the bolts that are designed to slide down the aero bars?

I'd recommend using the T slots, so easy and very secure. I've never tried the clamps as my aero bars (VW) are too deep.

mine's held on with string…

(not kidding)

no problems in 3 years.

There have been reported failures of the T-pieces – although I've not read of any in the last 4 months…there were a few people on STW who posted about failures with them – personally I don't see how they are as secure as a clamp that goes all the way round the bar…the clamp in my view is more secure and is the solution I use – personaly choice though.