Magellen file conversion format - 4225


I am new to the GPS world. I would like to add more POI's to my Mag 4225 (COSTCO). Which format is the easiest to convert to the Mag file format and offers the most POI's? ... Garmin, Nuvi, etc? This site offers two; which do I choose? If I understand correctly, the icons & sounds can not be modified. Correct?

Mag Files conversion

Nuvi 2595LMT