You could wear it in the car, but it's more comfortable not to! It's definitely handy to wear during launching and recovery though as you won't have any worries about getting wet.
The Viking suit that Andy is selling is
a dry suit. There are dry suits designed for diving, and dry suits like this one designed for surface use.
The term "immersion suit" is sometimes used to mean a flotation suit like these
, sometimes a surface drysuit like Andy's, but most often they are "abandonment suits" designed for emergency use when working offshore. They are waterproof, and (unlike a normal drysuit) are thermally insulating. There's a good page of info here
if anyone's interested.
You've probably already had this advice but it's worth repeating:
1 Get a breathable dry suit
2 Get one with a fly zip