Agreed the Nvidia shield in its later updates to the OS really went heavy on the ads.
One way around this is with a OS downgrade and sticking with OS version 8.2.3 and not upgrading the home launcher, or replacing it with another launcher internally.
These were the steps I followed to downgrade all my Nvidia shield around the house.
https://florisse.nl/shield-downgrade/
Definitely on the lookout for a new media box though and the one you mentioned caught my eye as well.