Ask the guy what are the 5 things that affect VTEC engagement:
rpm, TPS, oil pressure, engine temp, vehicle speed
then ask him how the IM affects these...they don't.
what the IM will do is shift your powerband up higher and that's where you gain will be at the expense of midrange.
To compensate, you must tune the cam gears or ECU tune to get back some midrange. In most cases the VTEC is moved higher in tuning with this IM because of the fact that the air flow speed for the right air fuel ratio in the powerband occurs later.
That's what he is "trying" to say but really doesn't know how to say it. He's also trying to sell you the EMS. To be honest, I'm not sure if he knows the facts leading to the bottomline answer or whether he is just parroting the bottomline that someone else has told him back to you.
Of course, with any new part, you will need to tune...that goes without saying. Tuning with an EMS is ideal. Do you need one right now, right away or the Im won't work? no. You may have a hole in the midrange to fix but you can fix that with a fuel controller, FPR, ignition advance, and cam gears.
you knew the single stage IM would shift your powerband up right? Are you going to stick to a 62mm TB or a 64mm TB?