A New Zealand invention and thus a lot of them in my neighborhood.
They're said to be soundly engineered and good quality but for me, the advantage unless you have a property right on the water is dubious.
They travel over land at a walking pace so for anyone not living on the water, a trailer would still be required to get it from one place to another. So in the true sense of the expression, they're not really amphibious as claimed.
And I believe them to be frightfully expensive.
The manufacturers have, I understand, achieved a significant military contract somewhere. I can't imagine trundling up the beach at 5 kms per hour while under hostile fire.
If you want to see a truly amphibious vehicle, have a look at this one.
I've actually seen someone water-skiing behind one of these in Auckland (there is a video clip on their website) and on land they're a normal sports car. But I believe that also due to military contracts, they have been withdrawn from the market (not researched, just rumoured).