https://supr.com/mode-machines/products/cerebelusb-usb/
Will i be able to send midi both ways? (Just tempo sync) so use the op-1 as master, or the other way, slave it to incoming midi clock?
would the more often mentioned Kenton usb host be a better choice?
I know theres some info on the subject but i can’t seem to find a clear answer.
Cheers 
The device you linked to only has a Midi Out so it won’t send any Midi back to the OP-1. Since this is based on an Arduino though and since there are still some free pins available, according to the description, you could add Midi In yourself. In order to do that you should be comfortable with soldering and programming though.
The Kenton USB host has both In and Out ports and will do what you describe.