Many 'free flowing' filters suggest better air flow & better performance yet suggest rejetting or fuelling mods are not required which is itself contradictory....
The Lambda sensor controls fuelling at tickover, low revs and light throttle (closed loop), at higher revs the bike uses the factory fuelling map with adjustments from various sensors on the engine like air & water temp, throttle position and manifold pressure (open loop), in open loop info from the Lambda is not used.
I've never understood why bikes have never used a maf sensor like in the automotive world, maybe it's not feasible to fit one in the small space between the air filter & intake, on a motorbike?
Slight changes to the intake and exhaust side should be dealt with by the bikes electronics.