Jeremy: It all seems to be down to your lack of experience with e-bikes. "American specification" means Class 1 and Class 3. Both classes are limited to 750 W of motor power; Class 1 is limited to 20 mph/32 kph (typically, e-MTBs) while Class 3 is limited to 28 mph/45 kph. New Zealand allows up to 300 W but there is no limit on the speed in your country. (We are not that lucky in Europe, as a "Euro e-bike" means 250 W nominal, 25 km/h. We also can ride 45 km/h "mopeds" under certain conditions in Europe).
Having said the above, I need to note that four biggest e-bike brands (Specialized, Trek, Giant and Cannondale) as well as expensive -- but popular in NZ -- Riese & Muller offer 250 W nominal mid-drive e-bikes that are available as Class 1 or Class 3. Meaning, a selection of a 28 mph/45 kph mid-drive 250 W e-bike of Class 3 is a popular NZ choice.
Just slapping a Chinese motor, battery, controller and display onto a traditional e-bike is doable. My earlier question was simply whether you had ever considered buying a good manufactured e-bike, taking into account how liberal the NZ e-bike law was? An e-bike that was designed as an e-bike from the scratch? With safe and nicely integrated battery, classy motor, and excellent electronics? With hydraulic disc brakes and adequate drivetrain? With ride comfort and safety in the first place? There are several other Kiwis in these Forums, and you could just ask them.
I asked my question because I had considered a conversion of my existing traditional bike myself. Luckily, I learned about the benefits of manufactured e-bikes early enough.
