If thats the only light on you DON'T need any cleaner! Take it for the drive I suggested.
Extract from factory information:
45% DPF Load Level 1
Normal Regeneration
50% DPF Load Level 2
Regeneration at maximum exhaust temperatures
55% DPF Load DPF lamp
Regeneration from 60 km/h onwards
("See operating manual")
75% DPF Load DPF, SYS and MI lamp
Torque limitation, EGR deactivation,
Regeneration via VAG tester only
95% DPF Load Replace the DPF Unit