shuggie wrote

Can I directly access DB to get client's information?

Sure, why not? But I don't know whether EAPs send the data as often as every 10 seconds. You have to find out for yourself.

Create a script:

$ cat >clientStats <<-\HERE

#!/bin/sh

case $# in
  0)    query="\$and: [ { site: 'Default' }, { duration: { \$ne: 0 } } ]" ;;
  1)    query="\$and: [ { site: '$1' }, { duration: { \$ne: 0 } } ]" ;;
  *)    echo "Usage: ${0##*/} [site]"; exit 1 ;;
esac

mongo --port 27217 tpeap --eval "
db.client.find(
                { $query },
                { ssid: 1,
                  mac: 1,
                  snr: 1,
                  rssi: 1,
                  download: 1,
                  upload: 1,
                  duration: 1,
                  _id: 0
                }
        ).sort({ mac: -1 }).forEach(function(doc) {
                print(tojson(doc));
        }
);"

HERE

Run it:

$ chmod +x clientStats

$ ./clientStats
MongoDB shell version: 2.4.10
connecting to: 127.0.0.1:27217/tpeap
{
    "mac" : "00-17-F2-XX-YY-ZZ",
    "ssid" : "Radio Moskau",
    "snr" : 27,
    "rssi" : -68,
    "download" : NumberLong(4430),
    "upload" : NumberLong(12332),
    "duration" : NumberLong(186)
}
$ 

If you modify/enhance the script or add a nice graphical representation of the results, please share with the forum.

For installation of Omada controller on a RasPi see this thread. The thread [3] you linked to is way too old.