Hansgrohe bar mixers aren't massively expensive, I feel I could easily talk the customer into the cost difference on the basis that its top of the line, almost faultless and with a really good back up. Even more so if you're doing drencher heads which means holes in tiles for fixings meaning you don't want to be replacing it in a few years when it inevitably fails.
I once fitted a cheap screwfix kitchen tap for a customer who wanted to save money and it failed just after the 12 months warranty. Never again will I talk customers into brassware which isn't well branded.