Do people tend to just screw thi s in hand tight. I no a lot of instructions say this. I do tend to like giving a tiny nip up after if they is space to get a spanner in.
Being an o-ring it seals by its position, being trapped in the groove and within the female tapping on the tap body, not by how tight they are done up like with a washer or compression fitting.
As long as the flexi cannot unscrew, which it can't because it is fixed firmly at the other end, hand tight is as good a seal as doing it up with tools.
That 'wee nip with a spanner' after years of hot and cold could mean it needs destroying to get off at a later date. Completely unnecessary in my opinion. As above, the o-ring makes the seal. Hand tight only for me every time.