Does the Eco functionality have any effect on reducing the router speed?

No. Download speed, connection quality and range are the same as for ordinary wifi routers.

The real speed measured with for the JRS Eco 100 D1 and D2 models is 400+ Mb/s. These are real measured throughput speeds, not theoretical values like ‘AC1900’.

The speed is the same as with the stock Asus firmware.