I don't know the answer to the blind question but are you aware that different patterns of obscure glass have different levels of "transparency"? There are documented levels of privacy ranging from 1 to 5 for each of the different patterns available with 1 being almost transparent and 5 being...
If you can afford the Pegler one then use that. In a years time you will have forgotten about the £5 extra cost but will have a valve which works reliably.
Edit: The last cheap one I had at home dripped water into the electrics of a fridge and I had to buy a new valve and a new fridge. :(
These units work well when you can't persuade people in the property to ventilate it properly. Fresh filtered air is introduced gently into the property to displace moisture laden air. The air circulates around the property via gaps under doors.
I find that they push air from upstairs to...
The biggest items in common use which must create safe zones (or we would not be able to get cables to them) are consumer units and electric showers. The safe zones for these items must be as wide and high as the item because, without removing them (or their covers), a person will not be able to...
Perhaps we could start with the common case of a wall mounted extractor fan. Does the extractor fan create safe zones above, below and to both sides which are the same width and height as the extractor fan?
The last house I sold had new tiles and felt to replace old pan tiles without any felt. No BC involvement. No queries relating to the roof during the sale.