Hi Cynthia,
I haven't used Engenius 202WAP, but I have used EAP600 which is an indoor, dual-band N600 AP.
For a side-by-side comparison, I have taken about 20 minutes looking at the important features of the Engenius 202AP and Nanostaion M2 and I am not entirely surprised that they almost look identical, both in external form factor and even specs - Max Tx Power, Gain... I have simply looked at two pages with specs for the devices. I actually think Engenius is some clone of Nanonstation...
The main differences would come up when you look at them from the management interface - because NSM2 uses AirOS while Engenius uses luci. So you will get different options for monitoring/management. For instance, I liked an option in luci (from EAP600) which allows me to schedule a reboot of the AP...
I know I have not quite answered you as you may have liked, but that is my 0.00001Bitcoins worth..