A chain is no stronger than its weakest link. - Thomas Reid
This section is common to both the EM 5.7 and EM Race models. Both bikes use 128-link DID chain. (DID is also known as D.I.D. or Daido Corporation.) The 5.7 comes with an FJ428H chain, whereas the Race comes with an FJ428NZ chain. Both types are supposedly available in either a gold or a natural finish, but you may not find stock on all variations. Beware, DID also makes an inexpensive “standard” 428D chain which is only suitable for something like a child's minibike. Chain with the NZ suffix costs nearly twice as much as the H suffix chain, and their life indices reflect this.
The FJ prefix indicates a press-fit master link. This is the type that comes directly from EM. Although this is arguably more secure than the hand-fit type of master link, it causes a major inconvenience during maintenance or if you must push the bike any distance and want to remove a chain in the field. I also prefer to remove the chain when washing a bike
To satisfy this requirement, I bought some hand-fit (RJ prefix) master links. The 428H and 428NZ master links have the same dimensions. I purchased a gold link for use on a natural chain and a natural link for use with a gold chain. This makes it easier to spot the master link while applying chain lube.
By the way, my favorite chain lube is Motorex Off-Road (part number 302280). I like it for two reasons. Firstly, it has low VOCs, so you can apply it indoors without feeling sick. Secondly, the spray button allows very fine control over the amount dispensed. You can literally get only a few drops at a time, if that's what you want. This is great because I like to apply a small amount to four places on each chain pin (both inner and outer surfaces of each side plate). Yes, this is a bit tedious but indiscriminately applying chain lube to a bike running on a stand is a good way to contaminate the rear brake.
The part numbers for DID master links from different vendors may not be completely consistent. The information compiled below should point you in the right direction. It seems that if there is a G in the part number, it is a gold-colored chain or master link. A gold chain provides better corrosion resistance than a natural (black) chain.