There are risks to that because you are sharing a ring main so could overload it, and the protection (RCBO or whatever) is not bidirectional so could get damaged.
Almost entirely theoretical but if a million people install them 1 in a million things start to matter.
Ecoflow originally provided kit with a plug, got told off and changed to a plug lead marked "do not use" 😀 and a lead ready for "wiring in" cut for a plug!
New kit just has a wire cut for a plug