ABS on a 650GS?

[LadyAth]

I bought my bike without ABS and I have read differet opinions on the all-knowing Internet about if I should have it fitted or not.  Some say it is essential for tar riding, others claim that it causes problems when riding off-road.  Since I intend to do both, what are my options?  Can ABS be switched off easily for off-road?  Is it very expensive to add on a 2001 model?

 

[Adventurer]

 

[tok-tokkie]

 

[lecap]

 

[blazes]

 

[Chrisl]