The reason for using a TSDB is the space efficiency and higher speed a dedicated solution can bring over a generic database.
TSDB are meant for streams of data coming from different sources when usually, the writing load is much higher than the reading load. Sensors, for example, send data routinely but querying them usually occurs at lower rate. For specifically, a server might log CPU and RAM levels every 1 millisecond but will update MIN, MAX and AVERAGE levels only every second.
RedisTimeSeries is able to do some aggregations on the server-side which make aggregations queries super fast and simple. It also allows for automated retirement of data so if data was aggregated into the required measurements, the raw data can be erased.If simple API and speed are what you are looking for, you should consider it.