Phresh duct silencer good or no?

That's a great idea that they do this. Firstly, fans are noisiest at full power, so if you can use a variable speed motor control, you can run at 1/2 speed. Unfortunately we've all heard the electronic noise / hum come from some fan / controller combos. I would assume they have this dialed in so the controller better matches the fan motor so as not to introduce this noise.

For exhaust you may need to light proof the exit. I use a 9 " ball bearing exhaust mounted directly to the wall on side of house. I had to build a box to cut the light. I'm on an acre so it's not possible for people to locate where the small amount of sound is coming from. If it were needed to make it quieter the inside of the box could be lined for more sound dampening.