It's almost always available for less than the 'standard' price. Priced about right at the low price, much too high at £799. Quite a small capacity battery; remember battery capacity is one of the biggest costs of any kit. Reports on support seem to be that it is patchy (you need to dig deeper on that, just relying on a not very reliable memory). I wouldn't like the weight of even a small battery on the handlebars.
I would go for a kit from Woosh; for example
https://wooshbikes.co.uk/?hubkits#xf07kit which costs only a few pounds more (maybe less, not sure on Swytch postage charge). It is less neat with a downtube battery, but larger capacity battery and much better support.
If you went for Yosepower you could get a kit for a little less (along the lines jokskot suggests; his post crossed with mine.
Do NOT be tempted by the cheap direct drive units on ebay, mostly with big power ratings like 750w; heavy, inefficient for almost all real usage, and need an expensive battery. Search around this forum for more on that. Oh yes, and illegal for almost all real usage.