Well, first of all it's not that much more expensive than building a system yourself, I think in GN's video they calculated about a $70 difference from similarly spec custom build, so you're paying $70 for:

• Smaller form factor
• CEC
• Console experience (without losing system access)
• Idle mode with almost no power consumption and fast wake
• Resume/suspend functionality like on the Deck
• Quieter system

And the downsides are:

• Slightly worse performance
• Less upgradability

At the end of the day it's a personal choice, I won't be buying one at that price since my desktop has already become a console like system. But if I didn't have one I think it's a fair value considering how much parts are now, and the features it provides vs a custom made are worth it for me.