If you really, really need the bike , fine ride it till you sort it... but the fueling will be off, if you don't sort the O2 sensor. Plus if something else goes wrong the FI light is already on and will give no warning.
The eliminator is going to be the cheapest.
Personally, whenever I change intake / exhausts from std I always get a dyno run to confirm the fuelling is OK , if running too lean it can burn the valves.