My friends and I in Norway have ordered many kits from GM and have always received the parts so basically, the risk is low but you might get parts that is not OK.
I have had the following problems: twice I got brake handles made of plastic that I did not trust but GM have dropped those and are no longer shipping them.
I recently got a bad 36V/16Ah battery and is still waiting for spare parts.
Also one person got a bad motor after 1 km ride, but he got a new motor within a week or two at no cost.
I believe quality control at GM could be improved but if you find bad parts they are quite helpful and will replace the broken items but it takes some time.
You should also be aware that the new European e-bike (EPAC) standard, EN 15194 will soon be a requirement for complete ebikes and the relevant ebike parts. In a few months I believe customs in some countries will start to check if this is the case with shipment containing electric bicycle parts.
I would also not recommend a 48V system, 36V is better as they are supplied ready made with battery casing and charger. The 1000W motor is also four times the legal limit, a 500W motor should be plenty (and only TWICE the legal limit)
Per