Operationally the AIP-SSM1 and the 4240 run the same software, so they work pretty much the same.
The AIP-SSM inside the ASA is less expensive alternateive, but becuase it sits inside an ASA there is more to configure and manage (the ASA plus the sensor), The ASA also has some built in inspections that may filter some traffic/attacks from being seen at the AIP-SSM sensor.
- Bob