Here's a plan.
Contact a couple of established mainstream fan makers, Xpelair, Manrose etc, and ask them what features/build quality etc their fans have which make them better than hydroponic-market ones.
At the same time, contact a couple of hydroponic makers and ask them what features/build quality etc they have sacrificed in order for them to be cheaper than the likes of Xpelair, Manrose...
Then go and buy a Soler & Palau TD500....
It's not that simple....some "hydroponic" fans are more expensive than their "bathroom" equivalent (so, hydroponics aren't necessarily cheaper). This really is a case of speculative labels marketing and prices depends on stock and shop policies - the good for us consumers is to know that the market is larger than they like us to believe....
Anyone dares to prove me wrong? (you are welcome).