My wife is diabetic and we have both been involved with WeightWatchers for the past two years - and I might add, successfully involved.
The only negative thing that I could say about Splenda is that it doesn't behave like sugar in baked goods. I note too, that Splenda markets a half-sugar, half-splenda product that gets around this problem. Of course, if you're diabetic, you probably wouldn't be able to use that product.
Aftertaste? Don't think so. I was sitting at the breakfast table one morning before my wife got up. I saw the packets of Splenda on the table and wondered to myself how it tasted. I opened a pack and dumped it in my mouth. Exactly like sugar except for the texture.
My hubby uses Splenda, as he needs to reduce his triglycerides, it is the ONLY sugar subsitute I have been able to get him to use and we tried all of the others. I don't use sugar at all, substitute or otherwise, it gives me a " sugar high" and then I crash (makes me sleepy). After 7 years, I don't even miss it, anything sweet makes me nauseous.
It's a lot closer to sugar than any other artificial sweetener that I've tasted but not quite the same. Of course I can also tell the difference between sugar and corn sweetener.