Nicked from their website:
Fuel cells can save up to a third of a typical home’s energy bill and CO2 emissions, with almost no SOx and NOx emissions. Current efficiency of 35-40% from traditional centralised power generation can be improved to around 50% without the transmission and distribution losses that occur through the grid. Efficiency can be improved further to > 90% if a Combined Heat and Power (CHP) system is used for heating water.
If the technology could be commercialised inside boilers once the home infrastructure is ready for it, that’s a huge market.
On its own, you could probably say its not very efficient, but it can be more efficient or cost effective than current power production.