This is algo trading, or execution optimization. They aren't measuring the market / order book and then reacting at high frequency. They are reacting at low fr

This is algo trading, or execution optimization. They aren't measuring the market / order book and then reacting at high frequency. They are reacting at low frequency and then the execution is optimized to minimize losses caused by market feedback. This is a very important distinction if you hold the view that HFT risks destabilizing markets.