I've been doing a little snooping here in China and may have found some interesting co-incidences....
1) Some websites on Alibaba/trade sites show E-Fun has a CEO of Aileen Tian...... Erato used to have an employee, Aileen Tian http://eratoerato.en.ec21.com/
I contacted E-Fun for a price list and obtained one back from Aileen Tian and an offer to visit her factory in Xiamen.
2) Mountain Chen claims to make ZAP bikes, others on this forum suggest they are made by E-Fun. Certain models may be sold by different companies.
3) EFun and Xiamen Zap appear to be both located in the same Industrial Complex in Xiamen. The locations on both websites are sufficently obtuse not to clearly identify the plant/office but they appear to be located close to each other!
4) A photo on the 'contacts page' of E-Fun entitled Testing shows a foreigner filming an ebike on a dynometer.....he looks remarkably like the Italian buyer Mountain Chen showed in some of his videos.
5) Shots of the bikes on the hill road appear to be very similar - maybe this is a common test road that everyone in Xiamen rides up to test their electric motor scooters!
6) EFun (Aileen Tian) and Xiamen Zap (Mountain Chen) will not ship locally to China, only overseas. I have emailled both because I am interested in long-term testing some bikes..... but I cannot see samples unless I visit their respective manufacturing sites (sic).
Now while there is not necessarily anything sinister about this, but it might account for the similar shapes of bikes and designs being presented by both companies!!!
Also be aware that many companies in China are literally 'bolting together' components they buy from other suppliers to produce many items (not just e-bikes!!!) so details such as fairing & body shape, light fittings etc are common amongst many manufacturers.
Many of the electrical components come from local suppliers, not necessarily the sales group....my e-bike in China has had 3 controller units re-fitted, all from different sources but same local 'ebike manufacturer'!!
Most suppliers will do customisations, add spraypaint and stickers to 'brand' for customers.
It is not illegal to have trading companies, agents, co-manufacturers or other 'arrangements' with companies in China or elsewhere....so I am not suggesting anything.
Just putting out the general info....read into them what you may!