An auto-bypass can only be used if the pump is set to a fixed speed. It is incompatible with proportional pressure as the bypass will open more as the pressure increases.
However, the flow/head curves for the UPS2 25/80 are 'flat' up to a flow of 2 to 3 m³/hr, which is equivalent to 23 to 35kW (at 10C differential) or 46 to 70 kW (at 20C diff), depending on pump speed. This means that any auto-bypass will be either open or closed all the time (depending on setting). So an auto-bypass, on its own, is effectively unusable with this pump in most domestic situations.
The way round this is to run the pump in proportional mode and have a fixed flow valve (e.g Taconova Setter) in series with the auto-bypass. The bypass will open at the required setting but the flow will be restricted by the Setter valve.
Thanks for your detailed reply. Currently the bypass in my heating system is via a towel radiator in a bathroom. Do you think it would be best to keep it this way or move to the auto bypass and setter solution?