Frank,
If you gain from it business wise, go for it. But the whole discussion seems rather senseless. It is like the client hires a carpenter (you) to build a new veranda for his house, but he only wants to hire you if you use a hammer of brand B, whereas you are used to working with brand A. Shouldn’t the client be more focussed on the quality and longevity of the veranda?
Harm Millaard