I just received Niche to use for my Breville Barista Pro. I set grinding setting to 7 and it was really fine. I was expecting extraction time to be long... but it did not give normal extraction but only few drops passing 30sec+... I had to stop extraction manually. Is Barista Pro incapable of extracting really fine grinds? Or is this normal for all espresso machines?

Sounds like you have the grind setting too fine. This video offers step-by-step instructions on dialing in a grinder:
Once that's in the ballpark, you can move onto Espresso 101: How to Adjust Dose and Grind Setting by Taste.