When it comes to the BO6040 the thing to remember is that it spins the opposite direction from the high speed, so you have to change your hand positions. With the high speed, rotary, polisher it's left hand on top, right hand on the tail. The contact patch, that is, the part of the pad where the majority weight is put against the panel tends to be top right, it's top left when using the BO6040. So, you use the Makita with your right hand on top and your forearm at about a right angle to the body and your left hand on the body with your index finger over the power button. You'll notice that when the machine contacts the panel, the pressure will be where it belongs.
As far as the Flex v. Makita, there's a major difference in the way the two machines achieve forced rotation. The Flex does it by interfacing the backing plate with the bell housing. The Makita does it by way of planetary gears. The Makita puts more movement between the pad and the paint, and is well balanced by design. This can be demonstrated by taking the counter weight handle off the Flex.
They're both good machines and I know people can get good results with either, but for me, it's hands down the Makita.
Robert