I don't know that company, but there is a lot of money to be made from the grants and subsidies.
Don't let them Register you as their applicant/customer until you have looked at alternatives. In my experience the Gas and Electricity companies provide a very good service and guarantee, even if you are not their customer, and are dependable companies. Look at their websites.
I am always wary of door-to-door salesmen and leafletters or cold callers.