From the small photo provided they do look like Siemens E283CC (relabelling within the Siemens concern was a normal practice; later also rebranding, but since E283CC was not produced in the East, this is of no concern, and absolute majority of Siemens-made E283CC were of the frame grid, E88CC-plate-like construction, so practically impossible to fake). But ask the seller to provide photos of the etched production codes to verify.
Also, if the design permits (E283CC can be pushed slightly harder than usual ECC83), changing the wiring of the socket to ECC83 and using special-quality ECC83 variant would be probably still cheaper, plus you can even select better specimen from a larger pool of tubes... And, also ensure you will have spares in the future.