I wouldn't want to work on something that is held with a lifting device.
I would prefer to get 2, 3, or 4 really good jacks and 6 axle stands. Lift it up, put the axle stands under the car and let them take the weight, then use the jacks as a fail-safe for the areas you are working under.
The flat jack would get in the way when working under the vehicle, which, presumably would be the reason for purchase and as Andy has stated, the Two-Post lifts would be too much hassle to install.