Under no circumstance will I fit a flexi under a bath. For a start, I have seen the damage they can cause over time, especially the hot side of it. If I quote for a bath tap replacement, then on removing the panel, find that the current taps are fitted with flexi, I curse my luck and redo in copper pipe but just foot the extra labour cost. In some cases, I tell the customer in advance that if I find flexis are fitted, I will charge extra to replace.
Even when I am fitting monobloc taps that come with flexis, I replace the tails with copper ones most of the time.
View attachment 16052 the image you see, is a bath tap fitted in Battersea, using a flexi on a gravity system fed from a CWSC. Not surprisingly, the cold tap takes for ever to fill. Now, if a copper pipe had been used, it would have leaked like HELL and flooded the flat below. So why not use a flexi? What a joke