Generac and Kohler are the same units. One of them makes it for the other company. I did not go with the whole house unit and saved $4K (about 5 years ago).
We have a well, furnace and about 3/4 of our 2400 sq. foot home on the generator. 2 fridges and a freezer included. It is a Generac 10kW unit and we have no issues at all.
Be advised, - a service contract is not needed. The installer wants $300+ for a yearly oil change and plugs/air filter. Parts on amazon run around $30 plus 1.6 quarts of synthetic oil.