BTW, here is a discussion about Polygon.io:
https://www.elitetrader.com/et/threads/iqfeed-vs-polygon-io.320799/
They are fairly new and also had lots of issues to solve, but I may consider them now too.
Though no one can really beat the downloadable Nanex tapes with highly compressed data allowing you to re-scan, re-process, simulate and backtest through years worth of data.
https://www.elitetrader.com/et/threads/iqfeed-vs-polygon-io.320799/
They are fairly new and also had lots of issues to solve, but I may consider them now too.
Though no one can really beat the downloadable Nanex tapes with highly compressed data allowing you to re-scan, re-process, simulate and backtest through years worth of data.