I have not used the EN2SE-R itself. My understanding is that it is a new generation of the HMS Communicator, equipped with a Rockwell DLR capable dual-port Ethernet interface, and with a configuration applet embedded into an Add-On Profile (AOP) so that it can be configured entirely within Studio 5000.
But I have used the original HMS Communicator, with the HMS Configurator utility.
For ordinary ASCII with terminating characters (like CR and LF), these are very easy to use. In the array of data that arrives as the I/O packet, there's an incrementing counter that increases by 1 to let you know that a new string is in the Input data array . Another element of the array is the Length of the string, and the rest of the array is the bytes in the string.
All you have to do is write code that essentially says "If InputCounter > InputCounterOld, copy Input data to String and set InputCounterOld := InputCounter"
The output is similarly straightforward; you copy the Length and Data bytes into the Output array, then increment the Output Data counter by 1, which causes the module to send that data out of its serial port.
In my opinion, the Communicator's ease-of-use is second only to that of the RTA Gateways; those send data directly to ControlLogix Tags that you configure by name in a web browser interface. The upcoming Spectrum Gateway works in a similar way.
I don't think it's speaking out of school too much here to say that HMS discovered a serious bug in the EN2SE and its related modules last year that led to a short stop-sales order and led me to use a competitive product. That actually makes me more confident in the current stability of the module and the competence of the HMS worldwide distribution and support network.