What, monkey, is the advantage of the smaller wheel racer In your opinion ( apart from BMX handlebars 
)
Man I hope you make that thing number 4 ebike in your garage
It's a little hard to explain in writing, you seriously just have to try a smaller wheel if you have alot of hills in your area.
I'll give you some dot point breakdowns of what I think they are good for.
1. Hills - I challenge anyone with dual drive/whatever with larger diameter wheels uphill. Find me lol
Also - complete dead start on hills is no worries.
2. Stealth. Riding a smaller bike people just think I'm riding a BMX (or a big one in my case) people see BMX's going fast all the time usually with kids without helmets. I've
never been stopped by police on this bike.
3. Control. Using a smaller frame you can pop wheelies over gutters easy, jump with control and the sheer agility of the smaller wheel moving around is far easier than with a 24-26-28" MTB
4. Stopping power - 20" wheels using regen really stop fast!! At top speed (need to test this) but I would expect as little as a few metres before I'm completely stopped using front disc brake and regen only.
5. Pedalling!!! You can do it these smaller wheels, you will pedal far faster uphill using direct drive and small wheel size than any larger wheel diameter ebike. Sure its no freewheel experience, I'll post this video I found of me pedalling dual drive so you can understand a bit better. It's like pedalling a high gear BMX (a bit hard to start, but feels okay once you are going)
So I can only really fault them with the top speed, and some difficulties depending on the bike frame you have. The one you have Ginge, sounds like a 24" BMX frame (the larger, pro type - still have 20" wheels) and these are quite comfortable to ride as an adult.
The handlebars (BMX Type) do make a serious difference to the ride, as being an ebike - the rider does not have a forward riding position (unless you are pedalling like mad), usually you are sitting on like a seat so the seating position for a rider on the BMX handlebars feels so much better on an ebike.
Should this topic not be surrounding ebike use, then it would be a COMPLETE different story with many benefits of larger diameter wheels (using gearing etc.)
If you want something that eats hills, fast acceleration and easy to manoeuvre then go for smaller wheels. If you can fit 16" wheels without too much difficulty on that frame you have, and are happy with about 30-35kmh top speed - then I would go for that!
If I managed to make the 16" work on the frames I had on hand then I would have stuck with it. I only went to 20" for ground clearance and frame size issues. The 16" when I had it running was VERY easy to pedal!!! Thinking back, I don't think I worried too much about the drag.
But yeah, long story short you gotta try it if you have hills, perhaps want to pedal a little, and don't mind about the top speed then I wouldn't look further.
Oh and tyres!!!! Seriously big range and with the GM cast rims you can opt for motorcycle tyres or scooter racing tyres like I did. Nearly forgot to mention tyres LOL they are tops
So 2 downsides...
1. Customising the bike to suit rider and accomodate wheel size
2. Top speed
