In my experience it works great at least for short term. At longer use periods I'm feeling like it might be contributing to getting to a too much of a relaxed state where I'm not able to get a good aggression for workouts and are kind of too relaxed in general.
The research I've seen seems to point towards rosavins being inactive alone, with their utility coming from synergy with salidroside and tyrosol, which are active. Can you point me towards some research showing that rosavins are sedating and/or their effect on serotonin? (edit: I'm aware of rhodiola's effects on serotonin, but I'm not aware of anything that conclusively shows that these effects are reliant on rosavin). I'm not saying I don't believe it's true, just that I'd be interested in exploring it further. Perhaps an alternate hypothesis could be that the higher rosavin extracts are often low in salidroside/tyrosol, therefore not providing the "energizing" or "anti-fatigue" effects that come primarily from the salidroside/tyrosol, and the sedative effects could come from some other (non-rosavin) components of the rhodiola, or perhaps be an interaction with something else people are taking with it, as even salidroside has been shown to be synergistic with some sedatives (i.e. it potentiated the effects of a sedative).
I ask about rosavin's effects on serotonin as some research has shown rosavins to be inactive, while other studies have shown salidroside to augment serotonin levels (as well as dopamine levels). I suppose it is possible that the rosavins augment the serotonergic effects of salidroside moreso than the dopaminergic effects, but that's something I'd have to look into further.
Rhodiola is an interesting plant. Higher doses of Rosavins tend to make me sleepy. Higher levels of salidroside give me a boost of dopamine. I like either 11% salid or 99% salid but the 99% is exceptionally expensive.
Also of interest is tyrosol. Salidroside is metabolized into tyrosol so you can think of tyrosol as sort of a super salidroside.