Hello there,
I recently acquired an ER-X and I am stress testing it at home, and I still beleive this thing is awesome for the price.
Web filtering with squidguard while transferring on a 50mbps link seems to crash the device hard almost all the time however. I know we shouldn't expect miracles from such a low cost device, but enabling web filtering without risking to bring down the whole network would be nice. I don't know if I may have missed something while configuring it, but this happened a few times at home.
Other than that, iperf tests are pretty much the same than my Cisco ASA 5506-X without Firepower enabled.
Image below, Left UP Cisco ASA 5506-X Firepower disabled, down ASA w/Firepower (URL, IPS and AMP) enabled. Right ER-X.