I disagree...YOU NEED IT! Especially if you are fitting new cans. IMO it is THE most important mod for the 9. It smooths out the throttle range, significantly improves throttle response, and allows you to customize your bikes mapping to your own liking as well as to your individual needs as far as altitude, temperature and equipment. You can get away without it, but there are many drawbacks. If the bike ends up running rich, not only will you get alot of popping on enging braking, but you could damage the cylinders by getting fuel into the fresh oil supply. Too lean and you start running hot which is just plain bad for all the engine components.
My advice is to get them both. I know it is pricey but it is worth every penny. Wait till you have saved enough for both or buy the pc first. Check out 919.org and see what LDH has to say about it. Without a doubt the most important mod, and coupled with a quality exhaust like sato, you WILL NOT BE DISAPPOINTED! I am sure the experts (m51142, LDH, ratdog, etc) will back me up on this one. Flatovercrest may very well have had good results without the pc, but everyone's results vary depending on the components and the area. Also, I bet it would be even better with a pc. Sorry for the long thread, just wanted to give you all the facts...hope this helps...not the wallet, the bike...good luck!