Although I'm not an expert, I can hover/harrier/TR, etc. Here's the biggest differences I notice:

There's seldom any wing rock in Realflight 3D type planes. Although some of the larger planes flown in real life (and electric foamies) may not rock their wings very much, planes under 30% are few and far between that don't have this issue. Some are fairly easy to deal with and others can get out of control fairly quickly.

The planes in RF seem to have a bigger "sweet spot" where they will start to torque roll, they're easier to keep there (especially true of most the planes you can download), and they don't spin very fast, making it easy to keep up with them. In real life some 40 size planes will spin like a top in a TR, and do so abruptly when you hit the sweet spot. Bout stained my shorts learning that one.

In RF there's absolutely no rudder coupling. A rarity in the real world, and a big downfall in realflight's design IMHO. Again, depending on the plane, in the real world this can go from no big deal to making things much more difficult.

In RF the ailerons don't work at 0 airspeed (are partially effective in real life due to prop blast). In general the wind effects and mass/thrust/inertia things that happen at slow/no airspeed are too easy in RF.

RF is by no means perfect when it comes to 3d, and some of the aftermarket downloadable planes do you no favors, but if you stick with a plane that will stall at a reasonable speed (not to slow), is fairly difficult to torque roll, and can't flat spin or do endless stationary waterfalls, it should be close enough to the real thing to prepare you to be able to do it in real life. It's just going to take more attention at the field, and you probably won't find it to be as easy. Hope that helps!