Most cheap measurement mics, sub $100 are the same exact microphone just rebranded.
It is my understanding, from attending a Smaart class, that roughly all measurement microphones utilize the same capsule, however they are different grades of it. The really inconsistent ones go to the cheap brands, while microphones that cost thousands each come from the batches that have passed several grading tests. ie if you are spending $2k a mic they will be fairly consistent microphone to microphone. If you spend less than $100 one might be extremely flat, the next may not be, it is anyone's guess.
In particular measurement mics that are under roughly $500 tend to be inaccurate above about 6K, again not all but many.
However this does not matter if your microphone has a calibration file. My measurement mic of choice is usually a Rational Acoustics RTA-420, with a calibration file ($150).
With the caveat that a microphones frequency response will deviate over time for for $150 that you have an incredibly flat microphone.
As someone who uses measurement mics in the field for work, I really like a $150 vs a $2,000 one as if someone drops it or runs it over with lift (it has been known to happen), I do far less crying in the aftermath.

