Traps for new players
Further to what PM said, the number one problem with amphibs is people landing wheels up on land or worse still, wheels down on water!
Amphibs also add quite a bit of weight, so you lose payload. There are a number of operators that have ramp or trailer setups for their straight floaties.
As far as eco friendly goes, there are lakes up in Alaska and Canada that only allow kayaks and float planes to access the waters so that speaks for its self.