I don't understand why there is timeseries solution there, usually people who use timeseries work with many Gigas of storage, are we gonna pay for RAM to do that?
First it all depends on your latency requirements and TP, if you need your TimeSeries DB to support high ingest TP and low query latency a RAM based is almost the only way you can go.
Second, many Gigas is what you get from any small size server...
And, on top of that Redis/TimeSeries supports an almost linear scale out which allows your memory to increase dynamically according to your needs.
Last, Redis Enterprise (& Cloud) add Redis on Flash support extending your RAM to your local Flash storage.
I have run Redis clusters, both with and without Redis on Flash, with hundreds of GBs of data. If you need the performance, it's doable and not prohibitively expensive.
Second, many Gigas is what you get from any small size server... And, on top of that Redis/TimeSeries supports an almost linear scale out which allows your memory to increase dynamically according to your needs. Last, Redis Enterprise (& Cloud) add Redis on Flash support extending your RAM to your local Flash storage.