Woosh have been selling electric bikes for many years. If they were no good, they'd be out of business.
All electric bikes work. I've tried literally hundreds, and I've never found one that I'd be unhappy to own if it were the only one I could have. Any electric bike can have/develop a fault, though most don't.
If you own an iphone and a wardrobe full of designer clothes, you probably won't be happy with a Woosh. If you have a Casio watch and like to shop in Aldi, a Woosh bike will make you very happy. That's about what it comes down to.
You were looking at Kalkhoffs because you thought they might be more reliable. They seem to have problems at the moment, but lets pretend that they didn't. You buy your Kalkhoff for £2000. Three years later, there's better bikes, so you want to change it. You'd probably get about £800 for it, so it cost you £400 a year. That doesn't include the cost of a couple of new chains and sprockets, which is more or less a certainty if you do many miles.
Let's say you bought a Woosh for £1000, and after three years the battery was knackered, so you decide to sell it. You'd get about £250 for it, so it cost you £250 a year. You'd be unlucky to have any costs for replacement parts in that time.
Which is best?