I will be looking at each of these in turn as time permits. I have a high respect for Giant bikes having ridden a Giant Expression with no problems whatsoever over a period of ten years. Remember that although batteries are expensive the bike without battery or motor is important too. If you buy an electric bike for £500, given that battery and motor will cost £400, you are not getting much of a bike. Giant frames, bearings, gearing are all excellent.
I;ve shown below the Giant range from Formby Cycles (Merseyside). Prices are pretty much the same everywhere, although check out e-bay where you can find ex-demo Giants at a good discount with full guarantee and minor cosmetic blemishes. Currently, for instance, Fulford Cycles have a good range on eBay.