This is a nice amenity but is not a smart model for disaster preparedness. People should rely on themselves, not a solar charger that may or may not work and may or may not be available.
I always have three phone batteries good for over a week of normal use, charged and ready to go. This cost me $22.
You can buy 10,000mAH external batteries / chargers for cheap as well.
If having a cell or tablet available is important part of your disaster preparedness plan, you should not rely on stuff you don't own that may not work and may be in use by 7,000,000 other people.