how useful are these tools in answering the only question that matters — being on the right side of the trend
Some traders use trend lines to determine this by aiming a longer timeframe. The longer time frame can really give you a longer direction. Maybe from, daily, weekly and monthly.
and how long is the trend likely to last?
I don't know if this can be known because sometimes, some traders say market has been over bought or sold but it does not revert. It all depends because before the reversion it can take more time.