JezFullham,
I just called Swiss Fittings regarding the BW Fittings: https://www.swiss-fittings.com/fittings/butt-welded-fittings
They only have these in material 316L/1.4404 according to EN EN10204, certificate 3.1, NOT in EN10253, I would go with SSE Pipefittings
I think most has been said above:
- Gate valves and Ball valves will probably be more expensive, as more material is used.
- Now switching from Ball valves to butterfly valves will need more initial pipe/fittings adjustments. (I assume the dimension are different, therefore additional cost)...