i have used, tried, and sold the three US versions and only the Yoyodyne has been 100% reliable after more than a hundred units sold (by me).
i tried another popular maker that offers OEM slave cylinders and got a 50% failure rate out of the first batch. as a value added bonus, one of them went to singapore, so that was extra shipping i got to eat. said manufacturer had no comment on the situation other than to blame the customers bikes. note that replacement yoyodyen clutch slave cylinders worked perfectly...
also, with yoyodyne, should the customer experience a failed clutch throwout bearing and this ruins the clutch slave, yoyodyne will replace it at 50% off. even though the failure has nothing to do with the clutch slave.
the yoyos are spendy, but sometimes, you get what you pay for.