Unfortunately, you have to give all personal details before you get the shipping cost, which could be anything. The total price won't be $499. It mentions $247 international shipping somewhere.
Another thing is that the $499 one doesn't come with a LCD, so I guess that means that you only get maximum power when you pedal, which can be a bit of a nuisance. That's if there is a pedal sensor. There's no mention of one, so probably throttle only, which can also be tedious. No point in having a LCD if it's throttle only.
There's no gears and the provided gearing looks quite low, so you won't be able to pedal much past 15 mph. That's a pretty inefficient bike without gears, so you won't have good pedalling efficiency either. That means something like 10 to 15 miles from the 8.8 Ah battery. There's no way it'll do 20 miles on throttle only, except maybe in a velodrome at 12 mph or less, when you compare it with the Woosh that has gears, pedal sensor, LCD and other stuff.
That leaves us with a £600 bike with a range of about 12 miles, no gears and probably no pedal assist. The price looks about right to me. £800 for the one with the bigger battery, looks a bit over-priced to me.