When getting extra magnets you will be able to generate even more light. Extra magnets will also help the generator charge faster. Depending on your type of SL200 light (with or without ReePower™) the outcome will vary.
In the SL200 type with ReePower™, the extra power will make the generator charge faster, and make the light a bit stronger.
In the SL200 type without ReePower™, the extra power will make the light flash both stronger and at a faster pace.