There are some differences in release directions, for example diagonal heel release on some tyrolias/Fischers/Heads, and pivot heels on old Look some modern bindings I can't recall (Rossi?). The cheaper bindings are simpler and don't have all the release mechanisms.
There is a difference in the material used vis-a-vis plastic fatigue cracks, etc.; gererally the more high DIN bindings are also built more robustly (too handle the higher DINS) and because they are over-designed for the lower forces will last longer.
There is a difference in elastic travel and re-centering, that is, how much movement the binding allow due to a shock load, like hitting a frozen rut at speed or landing some air, without releasing, and also how well and quickly it will re-align everything for the next impact.
I would recommend you get a higher DIN binding, but not one that doesn't include your Charted DIN. Whether you use the chart to get I,II, III, III+ or III++ is up to you, but once you have determine your DIN (based on boot sole length, weight, height, and how much you weight the cost of non-release versus the cost of non-retention), don't get a binding that starts higher than that and bump your DIN, just because you want that binding's features.
IMO, it's all right to be at the low end of a bindings range; you don't have to be in the middle. E.g. if your DIN setting is 6, go ahead and get a binding that goes from 6 to 17 (like Fischer FF17 +), but don't get a binding that goes from 10 to 20 (like Marker Comp 20) if your DIN is 8.