Can anyone using a vendor API like Nanex, Polygon etc. comment on why you are using their APIs instead of just using a much cheaper feed from a broker like Alpaca, TD Ameritrade, Tradier etc. ?
a) Most brokers will restrict the number of simultaneous stocks symbols that you can monitor in realtime for free. For IB, the limit starts at 100 for most accounts. You have to pay extra for more symbols.
b) My system monitors, in realtime, all NYSE and Nasdaq stocks. In the past I have tried Polygon, IQFeed and IB. On heavy days, at market open and market close, none of them could keep up with the quotes and fell behind by several seconds. Polygon was the worst, falling behind by more than 30 seconds on some days. I think Polygon made a fatal flaw using Json and Websockets. Easy to explain and to implement, but tough to get high throughput rates as compared to using regular TCP sockets and binary data.
Customers experiencing high latencies through our WebSocket feeds are almost always not able to keep up with the amount of data being broadcasted. When clients are not able to handle the throughput fast enough, our server-side buffer fills (increasing latency) until the connection is eventually killed.
We do not impose any limitations on the number of tickers you can subscribe to. We have clients taking down the entire market's quotes every day with no issue.