Hey guys..curious about a mechanical question...and hope someone with a mechanical background could help ???

Had shop professionally installed 2 bros. slip-on on the 08 CBR 1k and although it looks/sounds great I had a concern ?

I noticed of course on a cold engine the rpm's were high but after a few seconds the rpm's go high then low and then again, high then low until it levels at a little under 1.5 ...but the needle continues to dance just a touch..little... When I give it throttle it responds fine....

Is that normal..nothing to be concerned about or should I be worried ????? Just wondered b/c it's fuel injection and thought it should somehow run steadier...

Mechanic informed me that was normal and no concerns as a result of the removal of the stock exhaust....valve..open/close...issue ..more air/gas..causing increase

Any helps would be appreciated !