I use both the simulator and the Base modification+PC debugger, prefering the latter. I use PEP1 almost exclusively, so the Base modification is logistically easier. It also has the advantage that it does not care about extenders, and the PC debugger has some nice features to aid in session capture and logging.

The only issue I have seen with the simulator (I use only TCPIP, no extenders) is that I can not initially clear the socket. If I comment out that step I have no issues and it works..