slow wifi performance

What tool are you using to measure your speeds?  Instead of the Orbi site or app, use something like speedtest.net or their app to ensure accurate results.  Even apps on a small mobile device may not give you the best results due to hardware limitations.

Also, do not assume that because Comcast gives you "N" service then you should see "N" in the tool.  For best results, run the tool on a wired computer connected directly to your Comcast modem to give you a top baseline.  Then, you can compare wired and wireless speeds to your Orbi.

Finally, don't expect that your wireless speeds will match your top wired speeds.  Wireless has other overhead, encryption, etc. and other real world conditions that will limit performance.