Domus HP1 Humidistat/Pull-switch Extractor Fan.

I'm thinking of buying one of these for my bathroom but this particular version isn't a stock item at my local builders merchant so would have to be ordered. I've been on the domus web-site and can't find the info I'm looking for. Is anyone here familiar with these ? I'd like to know how the Humidistat sensor and the Pull-switch interact with each other. i.e. if the humidistat has kicked in, can I over-ride it with the switch to turn the fan off? Conversely, can I start the fan manually even when the humidistat hasn't kicked in?
Also, is the switch built into the fan housing or is it physically separate ? I want to install it in the wall rather than in the ceiling and this obviously wouldn't work if the switch was built into the fan housing.
Finally, regardless of the specific fan in use, should it be part of the earth-bonding circuit in the bathroom?
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