I took the plunge and bought the Oceania one since i do most of my flying around the region and have mixed feelings on it. I was already running Active Sky which simulates turbulence to a degree but not terribly realistically. This addon will work with or without AS but is designed to work best with it so i have been using it with AS enabled and with VATSIM weather since the default NZ and Aust weather stations in AS are very few. Overall i like the effect it provides and it has certainly increased the realism for me.
I recently flew from Milford to Manapouri/Te Anau and then on to Invercargill in some average weather. The increased (and realistic) turbulence experienced through the Alps and across the flat (ish) land between Manapouri and Invercargill was consistent with RL flights i have done. It certainly adds to a feel and has made me work on my landings a little rather than just flying the aircraft on to the runway since I am now getting little bounces and heading changes due to local wind effects that is was not getting previously. I think this is the most positive feature of this software/addon.
The downside for me is the higher level turbulence effect. I am not sure if this is the RealTurb or AS but at higher cruising levels there is turbulence even in clear air. Watching my G loadings the turb is pretty severe with fluctuations from 0.2 to 1.9 G almost instantaneously. I suspect this is the AS cloud turb modelling as i think it has been like this for a while and i have only recently added RealTurb. My AH2 passengers complain regularly about the max and min G loads during the flight.
There is a free Africa and Antarctica edition of RealTurb and if you are considering buying Oceania or North America i'd suggest grabbing the free trial edition first to ensure it does what you expect and you enjoy the effect. For me, it is definitely worth it, so much so i am going to also get North America even though i fly there very infrequently.