We have an old Xpelair fan that works well, but we got through about 5 solenoids (that enabled the louvered shutter to open and close) until they stopped being available in c. 2007. I was unable to find alternatives or get the 'broken' ones repaired, so it had been 'out of use' for some time.
This magnet, attached to to a simple bracket onto the opening striker on the back of the shutter enabled the shutter to be opened and closed in conjunction with a couple of small, circular (3mm X 6mm) neodymium magnets that attracted it from the front of the shutter. When the fan is not in use the 2 small magnets are parked on one of the 4 screws that attaches the shutter to the body of the fan, and the louveres close.
This isn't admittedly the most elegant of solutions, but it does enable the fan to continue to be useful and did obviate the need to make a hole through the face of the shutter in order to somehow open and close it via that route.
When they were available, the solenoids cost c. £64.00 each, rather more than the combined price of this bar magnet and the pack of 20 smaller magnets (I've now got 18 small fridge magnets) so for me I feel both items justify the high rating..