I cannot see an issue using a mortgage broker offered by the housebuilder. Just don't buy any add0ons like home insurance, mortgage protection insurance etc.
It is however VITAL you don't succumb to using the builder's preferred, suggested/recommended solicitor, under any circumstances, even if they offer you cash to do so or choosing one from their list.
The reason I resist naming the better housebuilders is because there will always be buyers who don't get a well-built home or give buyers poor after sales service. In addition, the better housebuilders today, can become worse next year. Seldom do poor housebuilders improve unless they are forced to by new legislation. I live in hope.