Kensa heat pumps are specifically designed to be installed by a plumber without any specialist training. They should be OFTEC or Corgi registered. (This is not a requirement of fitting a heat pump, however these qualifactions do show their that the plumber is competant).
The Slinky ground arrays are available as matched kits, direct from Kensa. Provided that the slinkies are buried correctly, and the heat pump and slinkies are sized correctly, Kensa offer a unique performance guarantee - that is not available from any other manufacturer or supplier of ground source heat pumps.
Kensa heat pumps are simply better designed than any other ground source heat pump. Their design makes them easier to assemble, which is why they can be priced more competitively than others.