Is there any source of an attenna booster for the Mavic Pro that will actually improve the flying distance?  The advertise 4.3 miles is misleading.  I fly in the city and I get maybe half a mile before I received intererance.  

You don't need a booster to fly few miles. You need LOS and no Wifi or other strong signals around.
Interference is what is causes this not weak  signal.

Bought a CP extender for my P3P from these guys, installed easily, boosted the advertised range by at least 50% non-powered model. The biggest benefit I see is in the Video D/link, virtually 1.5-2 miles out and video rock solid, mainly because of the circular polarization of the signal.

https://www.maxxuav.com/collections/dji-mavic-pro

Titan Atlas

Flew in the city and got 2 miles out of mine.

Just a word of reminding, we don't suggest using the unauthorized third-party accessories like antennas booster. If the connection distance between the RC and AC is short, please try to adjust the antennas, distance should be greater than height during flight, and please make sure the remote controller’s antennas are positioned parallel to and are pointed towards the aircraft, you can refer to the picture below. Sometimes the flight environment is also a big factor, fly in a wide place with less interference.
Of course, CE and FCC area has a different range of the distance.

DJI Thor Posted at 2017-11-26 19:40
Just a word of reminding, we don't suggest using the unauthorized third-party accessories like antennas booster. If the connection distance between the RC and AC is short, please try to adjust the antennas, distance should be greater than height during flight, and please make sure the remote controller’s antennas are positioned parallel to and are pointed towards the aircraft, you can refer to the picture below. Sometimes the flight environment is also a big factor, fly in a wide place with less interference.
Of course, CE and FCC area has a different range of the distance.[view_image][view_image]

Thanks for the info Thor.

While I am aware that reviews for cheap 10$ booster are quiet bad, I did get a SIGNIFICANT increase in range with mine. Pleasantly surprised.