???
Unless he has both microphones and does and A/B comparison, there is no way to know how far off it is. So actually... it would hurt to try. Because you know someone is going to do it, it will give results and a tuning, then they will think it worked fine and leave it. Completely oblivious to how bad it might have adjusted things.

It is bad enough that these things are only so-so accurate to begin with. I never trust them, I always manually set everything and adjust using my own RTA.
A/B comparison always shows the self-calibrating setup is usually off by a little. Usually not a deal breaker on most systems but depending on the receiver and room, can get some quirky results sometimes.
I often wonder how many systems are out there that someone has ran the self-calibration, it completely screwed it up, and it was left like that (by DIY & professionals alike). Because they lack the basic understanding or knowledge to know better and test equipment to verify.
I mean look how many people use an RTA app on their phone (no external equipment) and adjust systems with it. Not taking about an SPL meter app and just adjusting sound levels, they actually try to 'tune' the EQ with the mic built into their phone.