On the advice of Gibbs chairman Neil Jenkins to "go full throttle", and his deadpan assurance that "it is not possible to tip it over", I launch the Quadski into the water at an offshore test location.
Once afloat, I press a button on the handle bar to retract the recreational vehicle's four wheels. It beeps to let you know the operation is in progress, and stops when the wheels are fully up.
At that moment, I release the brake lever on the left and compress the throttle lever on the right - all the way.
The Quadski rears with a roar before lunging forward. And somewhere in the background, I hear the first few bars of the James Bond theme as the jet- powered amphibian heads for the horizon at an alarming pace.
The initial choppiness gives way to relatively smooth progress as the Quadski gets up to planing speed (where part of its hull leaves the water).
To avoid the risk of getting into international waters - a real possibility with the speed of the craft - I make a turn back. I fight the instinct to release the throttle lever, but the Quadski quickly proves there is no cause for worry.
With handle bar in full lock, I trace a wide arc that brings me parallel to the shoreline. In the manoeuvre, it feels safer and easier than in a jet-ski, although I must confess it has been a while since I last rode a jet-ski.
Aimed towards the east, I let rip to see how fast the thing is. But the Quadski hits the incoming waves at an angle and the sea spray that ensues makes it impossible to see the speedometer.
But it feels fast - very fast. Gibbs claims a top speed of 72kmh, which is about the average speed of a jet-ski.
The latter, however, has no wheels. The Quadski's amphibious capabilities allow you to go from land to water and back to land seamlessly - making it extremely versatile.
A hovercraft will do the same but it is bulkier and cannot scale steep slopes or grossly uneven terrain.
Unfortunately, a flat tyre prevents me from trying out the Quadski on land. And a broken fan belt rules out test-drives of the Humdinga too.
I am convinced though that there is a place in the private garage for both vehicles. Clearly, Gibbs and its distributor ST Kinetics will have to navigate a maze of red tape as well as bring costs down before they can hope to deliver any here.
The Quadski, for instance, will be classified a car here, since motorcycles are defined as vehicles with no more than three wheels. And it may not qualify as a car either, because it has no doors, windscreen or seatbelts.
The Humdinga's centrally located steering wheel (like the McLaren F1) will be a regulatory challenge. Its height (nearly 2.4m) means it cannot enter a number of covered carparks.
Lastly, its price tag (up to $1.9 million if registered as a private car) will be a hurdle for something that does not wear a Rolls-Royce or Ferrari emblem. Even if it can brave the waves to take you to Bintan for golf and back within half a day.
Nevertheless, I hope amphibious vehicles make it here. Being an island with waterways that go right into the CBD and heartlands, Singapore is ideal for such a mode of mobility.
Early owners will enjoy unhindered cruises. Late adopters might face a gantry or two over the Singapore River.