There is masses of stuff about Splenda on various threads. I think the two important things are a) you can cook with it, and the taste stays (unlike other sweetners, apparently) and b) some people react badly to large doses of aspartame or other synthetic sweetner.
Personally I don't like it much as it seems to trigger a sugar craving. Perhaps that is just because it is very like sugar.

As for the mushroom mystery. Who knows? I think it is possibly different kinds of mushrooms?? Different avocados are very different so maybe...

All the best