Fault Code Readers

[gazza0210]

Im thinking about buying a fault code reader for my 2003 W203 instead of getting stung for ££££ everytime the light pops up but have a couple of Questions :

Do I just need to get an OBDii reader or is there a particular type I should be looking for.

Also can these do damage to the Ecu when clearing the codes with the scanner.

Thanks for any help guys.