I haven't used erythritol but I've used xylitol, another popular sugar alcohol. It tastes good, kind of a cooling effect in the mouth, and it bakes very well, very easy to use, as advertised. It's fairly expensive, though. I don't know where erythritol is sourced, but xylitol can come from a couple of sources. The good stuff is made from birch trees, and it's expensive. The reasonably priced products are made from corn, and these can be highly pesticided and genetically modified. I don't know if there are organic corn-derived products available. I haven't looked because I've chosen not to use these sugar alcohols. Here's why:
First, they're highly processed products. I don't eat sweetened foods very often, so when I do I use a little raw honey, maybe some agave, maple syrup, blackstrap molasses, evaporated cane syrup. Personally I prefer less processing.
Second, high doses of sugar alcohols can cause diarrhea in just about everyone, but in some people, even tiny doses can do this. I have one client who can't tolerate any xylitol at all. So just imagine, you're invited to a party and you decide to bake a delicious dessert using one of these sugar alcohols. An hour later there's a line forming outside the bathroom because a few of your friends are intolerant. Honestly, I have no idea how many people are this sensitive, but this client made me totally rethink my use of these products.
Also, these are definitely not calorie-free. Some of them have significantly fewer calories than sucrose (erythritol), some are very close (xylitol). It depends on how sweet they are. They do help prevent tooth decay, though. However, if you have a problem with sugar--either with glucose metabolism or addiction--I guess I tend to feel that it's better to wean off sweets, to lose the craving, rather than find replacements. And if you only eat sweets occasionally, I'm all for going more natural. In fact, even with stevia, I now use the dried leaf, rather than the powder or liquid.