Low flow does make sense - presumably it switches off the boiler but
not the pump otherwise there is no means to generate a flow and
switch heat back on when the TRVs open again.

Yes. However there are some possibilities to avoid the wastage of too much
pump energy. Firstly, run the pump on a clock. Secondly, use a pump like the
Grundfos Alpha, which reduces flow automatically and avoids noise and
excessive electricity consumption. Thirdly, a device that pulses the pump
every ten minutes or so could be good, although I haven't seen an out of the
box solution for this.

Christian.