I use Sessions extensively. It is what makes Time Master valuable to me.
FYI, I have "Multi Timers" disabled.
I don't understand why I'm not allowed to edit the start time of a session when the timer for that task and session is currently running. I also need to be able to edit the start and stop times for previous sessions in a task when the timer for that task is running. Here's why: Frequently I forget to start the timer running for a different task the moment I stop working on one task and start working on a different task. I usually remember a few minutes later. It would be very helpful if, after I start the timer running on the new task, I could adjust the stop time of the previous task and the start time of the new task without having to stop the timer. I don't see any reason why you prevent that. I understand that I can stop the timer and then edit the sessions, but then I have to adjust the end time of the latest session to "now" and then restart the timer after saving the session, which creates a new session. All that adds complication, and it's not very user friendly.
Otherwise, I am mostly happy with this app. Thanks!