If you think you're a better than average driver, then it's probably worthwhile having a telematics device installed.
If you then drive within the parameters set out by your insurer, there's a good chance you could save money.
Likewise if you're not a "good driver" to begin with, but learn from the analysis provided and improve, then the cost of your insurance could fall.
There are no guarantees. If you aren't considered to be a good driver, and don't learn from the analysis, then a standard insurance policy may be a cheaper option for you.