The MK52 heatbed has embedded high Curie temperature magnets. These magnets are able to firmly hold removable spring steel sheets. The Spring Steel Sheet With Smooth Double-sided PEI uses the same PEI sheets as on the MK2/S. It is the best solution for printing PLA and it has great adhesion with almost all materials. The bottom of your prints will be smooth.

You can leave small marks on the print surface with your nozzle or tools, they will typically be shinier than the rest. It does not affect functionality or adhesion. However, if you want to have the same surface look on the whole printbed you can resurface it. The easiest way is to take the hard side of a dry kitchen sponge and wipe the affected area with a circular motion gently a few times.

Update:

The steel sheet color may differ from the product picture (black, gold, green, etc). The smooth PEI surface on the steel sheet, as well as all other properties, remain the very same for all color versions.

Find more details about the spring steel sheets in the knowledgebase.