The air cleaner your guy recommended is what Zipper's calls their "MaxFlow". It's basically the same thing as the old Screamin' Eagle air cleaner, but with a 1/2-3/4" deeper K&N element. You would need to buy a cover, either the Harley football or a custom cover, and the entire assembly would stick out at least 3/4" further than stock, which could cause some issues with your right leg. As for the flow rates of the two filters, I haven't seen any test results on either.
I don't see anything about that Zipper's part that would make me want to dump the HB. Of course, you could always tell your tuner to "prove it"; after he tunes the bike with the HB let him install his choice of air cleaner and make some more runs at his expense. If he can show you
significant improvement in curves and numbers (which I seriously doubt), and if you can deal with the drawbacks of that wider filter, go for it. It's not a terribly expensive part, about $115 retail at J&P for plain aluminum and $140 for chrome. Plus the cost of a cover, of course. Just have him give you a map for the HB as well, so if you decide you can't stand that Zipper's air cleaner you can easily reinstall the HB and the corresponding map without paying him again, and then sell the Zipper's parts.
http://www.zippersperformance.com/catalogue/showproduct.asp?cat=572&prod=2207Jerry