A DL9 medical is the most simple, quick and cheap medical you can have for private flying. The name DL9 comes from the form, which is primarily used for Driver Licence medical certificates. There are some limitations which you should be aware of to ensure the DL9 is the right medical for you.
The CAA website provides a table of flying privileges by type of medical certificate. It is important to read and understand the information in this table before flying on a DL9
Some insurance companies require you to have a CAA Class 2 medical for your aircraft insurance to be valid. This may be age-dependent. Check with your insurer.
Some aero-clubs apply restrictions on operating their aircraft for DL9 medical certificate holders. Check with your aero-club.
Some other things to be aware of:
While a GP can complete a DL9 you must tell them it is for aviation. Some GPs will not be comfortable to complete a DL9 for aviation.
The medical standard applied to a DL9 is not necessarily lower or 'easier' than the CAA medical standard.