Except for the datalogger feature, it has all the features of the Phoenix series---they are Phoenix ICE ESC's.
The 50 lite is physically bigger than the Phoenix 45---mainly due to the BEC chip which has a pretty big heatsink. Another detail is that the "Lite" weight doesn't include the wires--which are pretty heavy gauge wires, at least compared to the 45, so if you have extra length on the 45, it would pay to cut back the Lite 50 wires.
But I think the big feature is the built in datalogger. I paid ~ $90 for my Eagletree data recorder, brushless sensor probe, and a temperature probe. It is a big deal in my book if you don't already have a datalogger.