Hi there...
Now that's a tough question to answer straight up.
In one way, the polydextrose and the not/Sugar DO have similar purpose, in that they help make up for the lack of texture/lack of bulk of sugar, in recipes.
In another way, they are very different products and are used quite differently, basically because of the way they affect the other ingredients and cooking time.
Neither one is better than the other, frankly, because that would only be a good comparison if they acted the same way.
Example, I use the not/Starch in baking stuff (similar to not/Sugar, but slightly different and stronger results for texturizing/thickening/
gluten replacement). I also use the polydextrose in baking stuff, but when I do, I expect something more syrupy, it's more
sugar bulk replacement, but I also need to turn down the temp, reduce the moisture, etc., to take into account its water-holding capacity. ANOTHER reason to use Tried & True recipes when starting out, somebody else has figured it for ya.
On the other hand, if I want to make a syrup, or a candy, that kind of thing, I use the polydextrose, because what it really is most like is sugar texture without the sweet part (but it requires HEAT to dissolve it). So once I melt/cook it, it STAYS syrupy, not like Erythritol, which is sweet and will melt, but recrystallizes almost immediately on cooling. Yet I would use the not/Sugar for a quick cold syrup-like thing, like my own thicker maple syrup, or to make shakes, smoothies or lassis thicker and more "syrupy" and to add quick soluble fiber to my diet.
Then of course, there's the cost factor. By the pound, the polydextrose is cheaper than the not/Sugar and the not/Starch, but you use way more of it for every "application", the number of "servings" per pound is way less for the polydextrose, the not/Sugar and not/Starch last a VERY long time for most people.
Also, I use the not/Starch for stir fries, thin gravies (like jus) and savoury sauces.
Sorry, I DID say it wasn't an easy question to answer. Bottom line, I need and use all of them in my kitchen (but I love to cook and I'm LC for life). I consider them an investment, right along with the Splenda and the SugarTwin (in 3 forms
) and all the other stuff I have on my shelves.
Hope this helps
some.