Well do whatever makes you happy RX400h. If you believe that dropping in a K&N will give you substantial gains then do that.
Every company is going to try to sell you into their product regardless of if it works or not. This topic started out as "K&N air filter a good idea in the Rx300?", I'm here trying to word my opinion while trying to keep it Lexus related.
Prior to owning my current vehicle I was heavily involved in the import scene. Trust me, an air filter alone will not do you any good...dyno proven.
If you want to know why it damages MAF sensors then do a search. If you don't care then hey, what can I do about it?
On RX's barkat.