We purchased a number of these to use with some older 'mobil-truss' trussing that is 32mm in diameter. These couplers fit like a glove, the 3mm difference not being noticeable in the slightest.
The construction is very solid (and I'm sure highly durable) and very easy to secure. The angled lip for the locking bolt & wingnut means it is entirely possible to attach fixtures without assistance as once the coupler is closed the angle of the lip prevents them from undoing- very useful.
Also, the fact that the bolt head is recessed into the the bottom of the coupler prevents the bolt itself from turning (for instance under the momentum of a moving head fixture).
This main securing bolt (the one that attaches to the fixture) is a standard size, so it is easy to swap it out for longer items or in our case to use the bolts already fitted to a couple of our fixtures. This has been incredibly useful as it has allowed us to truss mount a couple of lights that weren't originally designed to be hung in this way, with no modification required to either the coupler or bracket- a great result.
The locking washer also helps prevent any rotation from occurring in the light fixture bracket.
Great piece of kit, and well worth having several spares around.