I think that's an excellent idea, however the item you linked looks really expensive for what is essentially one of those portable backup batteries for phones. You can find batteries that have nearly twice the capacity for a third the cost on Aamzon:
It seems to me that the only advantages to the Maker Shed model is that many development boards can be screwed down onto it, and it comes with a bunch of different USB cables. So I guess it really comes down to how much those features are worth to you.
The only other thing is, the Netduino may not be able to supply as much current through the USB port:
However, that could be saying that computer USB ports only supply 500 mA, so the 1A provided from the battery may let the Netduino supply its maximum current.