Somewhat gutted as this looks a great product. Wether it is worth the five hundred over the joule one is another matter, though.
We have just installed a 300l Joule cylinder. It works well enough. I did briefly consider the A+ rated OSO one, but could not get the energy savings to offset the additonal cost.
It takes 2 hours to heat to 52c. I have the flow rate set to 4 degrees above the tank temp at that time. Even when the tank reads 12 degrees we are still getting hot water out at 48.