This is true, it will depend on where the cooler is placed and if there is a way to remove the dust so it can flow without opening it. some models can be opened easily, in this case I would open. The best option is always to call a professional, but the cost of repairing can be high compared with the value of the tablet/notebook/computer. And if it is an old model most likely if one thing is repaired another will break, so then even if you are not a professional you might decide to try to fix as you can unless you have important data inside. This will depend on a personal decision. Even not being a professional on this clearly, I could remove dust from coolers because the service cost was high in a DELL notebook, also the original battery cost was 50% the value of a new notebook, so then I removed the dust and bought a generic battery, and bought a new notebook. I decided not to invest in an old computer and managed to extend its lifetime (probably not in the best way because it was not that easy to open this notebook model, but at least it did not turn off because of overheating).
What I would never do is to set the compressed air cleaner upside down, an intensive cold temperature might damage your computer. I would rather prefer to try to remove the dust than keep using the notebook with the dust, this will certainly burn the microprocessor and might be more risky. It will require common sense trying not to apply a very cold temperature (frozen) and find out how not to en-worsen the issue with the dust and get rid of it.
Shaking the cleaner will create more drops, I did that way because it seemed to be more intense, I did not know this could be harmful applied on the cooler surface, it will be certainly harmful if applied over other circuits directly. Just in case do not shake the compressed air cleaner.
