for every 1 invested BTC I will receive 6.25 BYTE? Did I understand correctly?
For 1 linked BTC (because you don't invest) will receive 62.5 MB (Megabyte) where 1 MB = 1 000 KB (Kilobytes) = 1 000 000 byte.
For each byte you have, you will receive 0.1 byte (+0.21111 blackbyte if your bytes are on linked byteball addresses).
What is traded for the time being is GB (Gigabyte) where 1 GB = 1 000 MB. For the time being 1 GB trades for around 0.08 BTC.