It is true that highly directional antennas (which none of those pictured in the ad are) can provide ranges such as they describe. Think satellite dishes and clear line-of-sight paths (or even better, put one side in orbit). But highly directional antennas are not going to let you "walk or drive around for a radius of around 30 miles" without stopping to carefully align *both* antennas every time you want to use the phone. With the antennas shown, even 30 miles over unimpeded water seems like it would be pushing it.
They offer only manufacturer's warranty (and it's not even clear what country the vendor is in). I don't know what Samsung model that is, but I'd bet that Samsung doesn't specify performance anything like that described. Don't do it without a full money-back guarantee.