With the MP1 the MFJ-934 artificial ground feature is not used. If used it will tend to steal current from the 33' counterpoise wire by causing RF current along the coax shield and the building AC power system, and/or along the "GND" wire attached to the MFJ-934.
An exception is if the MFJ-934 is placed right at the MP1 antenna with a very short coaxial cable (1' for example). Then the counterpoise wire is connected to the MFJ-934 artificial GND section and is tuned for maximum current. Trying to tune the MP1 and the artificial GND (they will interact) would be a challenge.
The MP1 uses a counterpoise wire and the antenna system should be setup to cause most of the antenna return current to take the path of the counterpoise wire or wires. To that end, the counterpoise wire(s) should be 1/4 wavelength long for each band. If that is not possible - and only one wire is used - a ferrite choke should be placed at the coax-to-antenna point to reduce coaxial cable shield current and force the current to take the path of the counterpoise wire. The bands where a 33' wire will be quite ineffective are 14 MHz and 28 MHz. On these bands the 33' wire presents an impedance of thousands of ohms the antenna return current will take some other path.
The chart by G3TXQ shows several feedline chokes that can be used. http://www.karinya.net/g3txq/chokes/
Note that the MP1 with a 33' counterpoise forms an asymmetrical dipole with the counterpoise doing most of the radiating. At 7 MHz the counterpoise wire "current-area" is about 23 amp-ft while the MP1 is about 4 amp-ft. On this band the counterpoise will do 85% of the radiating and should be placed as one would place a radiating antenna wire.
KH6AQ, formerly WX7G