Hey CarlD, I think the best times to get an SWG is if you are

A) buying a house with a pool and you are new to pool maintenece
B) Getting a new pool
C) a convert from baq
D) if you like the idea of having one less thing (bleach) to buy from the store and maintain.

I don't think you can necessarily look at it as a cost saving item... its more of a "less maintenece" thing. If you are on top of your pool every week.. and enjoy doing so, there should be no reason to change.