The factory eBrompton is ludicrously expensive for what is no more than a neatly installed front hub kit.
You could buy equivalent parts retail for about £500.
The kits mentioned in this thread are just as good and can be had for £1,000 fitted, and with the option of a lot more, er, options.
Brompton seem to think electrics on their non-customisable bikes are worth about £1,700.
Supply is another problem.
Despite the factory ebike being the height of ordinariness, Brompton seem unable to supply it.
Talk of the bike went on for at least five years before any appeared.
Even now, my local Brompton dealer has been told not to expect to see one until next year, although he was told some bigger dealers will get them sooner.