On the Westhill, you're paying about £300 for the hidden battery stealth look. for some people it's worth it. personally, I think it should have hydraulic brakes and a cassette motor for that price or it should be priced at around £1300. Hydraulic brakes only cost about £40 to upgrade, so that's no big deal, and you probably can't tell the difference between cassette an freewheel gears.
One advantage that the Westhill does have is its hub-motor, which is going to give you an easier time when riding on the road as long as you're not very heavy or have exceptional hills to climb.
Finally, if you're thinking that you might want a derestricted bike, make sure that you know the possibilities before buying. The Haibike can be done with a dongle that will cost over £100. The Westhill can almost certainly be done by pressing the right button sequence, which costs nothing, but you need to know the secret. Often dealers will give you the secret if you make it a condition of purchase.