Yes, there is, a tremendous differences.
Motorola accessories in this case the microphone, are specifically made to communicate properly with the radio. This is a two-way relationship between the microphone and the radio. The Motorola microphone was specifically manufactured to protect the radio in many real-life situations.
An example would be, if the microphone gets wet and gets a short circuit, there are tremendous circuitry and safeguards in place to prevent the radio from being damaged. This is just not the case with lower price generic accessories.
Trying to save $5 or $10 on accessories can increase drastically the chances of your two-way radio being destroyed, in fact, if you were to read the Motorola warranty, it specifically states that it is not responsible for defects caused by third-party inferior products.
But don’t take my word for it, this is a perfectly good example where a picture is worth 1000 words. You be the judge, want to destroy your radio that costs hundreds of dollars because you are trying to save 10 bucks?
Motorola Microphone on Left, generic on Right
Microphones Inside Picture
Motorola Microphone on Top, generic on Bottom