I own and use both the Wimbeley Gimbal and the RRS PG-02 Full Gimbal (Not Side Mounted), I would agree though with Nuero that the RRS PG-02 is the better unit, breaks down into pieces for better storage, although slightly larger it provides a slightly smoother experience than the Wimberley, but it is quite a bit more expensive.
As suggested by others, look at using a Levelling base on either unit, I use the RRS TA2 when using the Monopod Safari Rig from RRS, and the RRS TA3 Levelling Base when using the RRS TVC 33 Tripod. Look at getting the Levelling base with a Hook, very useful when set up on the Tripod, you can hang gear off the Hook either to be out of the way, or as extra downforce in wind, I use the hook to hang gear such as the Quantum Battery Pack and Promote Control when doing Long Exposures.
RRS I believe make the best gear out there in this Arena of Camera support etc, they're clearly not the only Player, but the degree of thought and fine Engineering that goes into their products impresses me and works well in the Field.
What ever you do, DO NOT download the RRS 2013 Catalogue, it will only lead you to the poor house.