I have an airforce 2 silent fan ( now Isomax). These hypers and cans are all much the same. Just a quality inline inside a silencer, the silencer is just some acoustic foam. Its ok for air sound, shite for motor hum.
They are good but stay away from ones with built in speed controllers. Buy bigger and run a variable transformer, use over sized duct and filter and its all good.
These steath fans are still rated at 50-55db, some squirrel box fans are as low as 30db. If I were buying it all over I would go with box fan oversized and turned down.
Mine is boxed inside a fridge box, surrounded by RWA, So is my Ruck for my veg tent.
I hate noise, used to make me paranoid, its no issue since I soundproofed everything I could. Loudest thing in my room is my tower fan.