As I stated in an earlier post:
You can actually use either one. With that said, if the pipes you have or are wanting to get have the bung for the o2 sensor, Then why not just get the closed loop one. You already have the stuff in place so use it. Plus it is better for the environment( so they say). If the pipes you have or want do not have the bung for the 02 sensor, then do not get the closed loop setup. If you have the o2 sensor bung and choose to not get the closed loop, just leave the o2 sensor hooked to the pipes and disconnect it from the connector under the seat. If you try to run 02 sensor and the FI2000r non closed loop together, the computer and the FI 2000r will be fighting each other for the proper fuel ratio.