This device is way overkill. You don't need a full router at all for the tablets, and USB wifi stick with an antenna connection is a far better choice.
The choice of antenna is also particularly stupid. Not only does it make very difficult to find networks (high gain antennas get their high gain because they receive from a smaller angle, so that this antenna will be difficult to point at an unknown signal), but there are antennas designs with similar gain which are far less conspicuous. A simple waveguide or microstrip sector antenna would be a much, much better choice, for example.