Like I said, it has merit in specific use cases, but in general, it may not be cost-effective. If you can add some functionality to it beyond just a power button, it would be more viable.
A couple of ideas come to mind. First, software integration with the Pi so that you could control multiple individual miners and power-cycle a stuck one, or turn on additional miners at set times, when power may be cheaper. Also, Crazyates mentioned auto-power-on; that got me thinking that it would be nice to automatically power on the system as soon as the power supply is plugged in, so that if power goes out in your area, you wouldn't have to do anything to start up your miners after power is restored.
Side note, I went looking for a cheaper alternative to that breakout board ($9 each, plus about $10 to ship), and I found
this item on eBay. Functional, but certainly not elegant. The guy sells them for $5.50 each, or five for $19, with free shipping in the US.