The first 24 bits (3-bytes) of the MAC are the identifier number of the manufacturer (e.g. Espressif) and the second group of 3-bytes (24 bits) is usually a serial number assigned by the manufacturer. So assume they always use the same manufacturers MAC prefix then you have a 1 in 2^24 chance of a part number collision, so that's a 16,777,216 to 1 chance of a collision and I doubt they have sold >16M parts yet, but maybe they have! even so the chance of you purchasing the same 3-byte serial must be so low as to be approaching zero.