I used a pair on my ST4s and thought they were fine...
until I was riding back from seeing one of the last flights of the Vulcan and met a sudden loss of power and a horrible rattle which I immediately knew was the sound of valves hitting piston.
I had installed the belts myself, and it was my first service task with a Ducati. I might have missed something - I don't know, but everything seemed to be in place and functioning. After completing the task I did have a pause for thought about whether I had the tension setting correct on the horizontal belt, but failed to open it up again to check, so the failure could be down to my initial oversight followed by laziness and my keenness to ride.
Upon inspection the belt had split longitudinally and frayed, at the same time stripping some teeth. I am considering sending the belt back to Dayco for their own analysis (when I get round to it), but on the positive side the vertical cylinder belt is fine!
Dayco belts are used on a number of high end cars, and seem to be well regarded. I probably would give them another try.
If you are going to try them, you might want to try a seller called 'Busters'.
These are what I bought.
Engine - Busters motorcycle Accessories
Good price when compared with Ducati - who let's face it are unlikely to make their own belts.
I know someone will be tempted to chime in with smart remarks such as 'you get what you pay for', and 'Cheapskate' etc., but please keep these to yourself. I have presented this as my own honest experience in order to help others make an informed decision.
I'd be more interested in finding positive experiences of these belts, tbh, and whether others have had belt failure on any brand including originals.
Seasons greetings to all!