Thank you fellas.

The Paige (screw fitting not click fitting) cannot be cut down to make a partial capo - but it might work as a general 12-string capo. I'll try one! The Tak is a VERY slim (front to back) and narrow neck though so there may be other problems.

John Barden used to use a glider on his Fylde. It DID affect tuning (but he was an approximate tuner at the best of times - his magnificent voice was his greatest strength).

The Thalia is very pretty but it appears to combine ALL the design defects I've been on about, other than the centering back bar, in one overpriced showoff package. Camber - non-adjustable. Gape - limited. Spring tensioned (as far as I can see) and flat fronted pads so very likely to bugger up tuning. When used as a partial capo - no access to the un-fretted strings.