conflicting information on bathroom fan in zone 1.

If the supply to the fan is RCD protected, the thinking is that the RCD should greatly reduce the risk of a lethal shock to earth for the occupant of the bath. However, IP44 is really about drizzle and occasional plashes, and I imagine Manrose  technical authors want to eliminate the risk that a slip with the shower head may lead to far more water than just damp air and droplets, and protect them selves against being held responsible for the effects of  a continuous stream of live water trickling down the tiles into the tub.

If it is installed in a way the makers actually forbid, as opposed to just do not recommend, then that needs to be take seriously.

So how dangerous is it really, 150mm horizontally does not sound like much - but is there any vertical clearance as well or is the intake at (or below ) the upper shower head height?

Some vertical offset takes it from credibly dangerous if at or below shower head, to not really an issue once about a foot above.

Even if you decide it is not a danger now, it should probably be a remark/observation on the paperwork so the owners are made aware the makers do not recommend it in that situation, if nothing else it may fail prematurely, and when replacing it a 12V model intended for such a location would be recommended.

If the supply to the fan is RCD protected, the thinking is that the RCD should greatly reduce the risk of a lethal shock to earth for the occupant of the bath. However, IP44 is really about drizzle and occasional plashes, and I imagine Manrose  technical authors want to eliminate the risk that a slip with the shower head may lead to far more water than just damp air and droplets, and protect them selves against being held responsible for the effects of  a continuous stream of live water trickling down the tiles into the tub.

If it is installed in a way the makers actually forbid, as opposed to just do not recommend, then that needs to be take seriously.

So how dangerous is it really, 150mm horizontally does not sound like much - but is there any vertical clearance as well or is the intake at (or below ) the upper shower head height?

Some vertical offset takes it from credibly dangerous if at or below shower head, to not really an issue once about a foot above.

Even if you decide it is not a danger now, it should probably be a remark/observation on the paperwork so the owners are made aware the makers do not recommend it in that situation, if nothing else it may fail prematurely, and when replacing it a 12V model intended for such a location would be recommended.