How does the Cisco MSE 3300 series differ from the Cisco Wireless Location Appliance (WLA)?
Check out this link on CCO for more infomation:
In essence, the MSE has more comprehensive location tracking capabilities such as TDOA (Time Difference of Arrival) as well as RSSI (which the WLA supports).
However as well as location capabilities, it also provides some integration to the Cisco FMC (Fixed Mobile Convergence) solution for delivering call handoff between mobile handsets with dual GSM and WiFi support, and Wireless Intrusion capabilities when APs are deployed in monitor-only mode.
The two MSE versions differ in how many devices are supported on a single unit, with the 3310 supporting up to 2000 and the 3350 up to 18000.
Hope this helps.