Yes I have one, I installed it about 2 months ago.
All I can say about it is it just works there is no feedback to the other boilers at all apart from a very slight warming to one boiler that’s higher than the rest. I assume its convection but hardly noticeable. I paid £150.00 from plumb centre and it’s the square one if you want one and cant get to that price let me know an I will buy it for you and ship it to your local centre.
I have expansion / air valve off the top, oil boiler and biomass boiler connected one side and heating from the other. One set of ports is blanked off as I don’t need it.
I have 3 pumps one connected to each circuit and interlocked with pipe stats and relays it is very easy.
www.dunsleyheat.co.uktel: 01484682635
Regards
stephen
see also biomass section