No info on the EECT900, I have a Power Probe 3. It will not load a circuit, that's what Load-Pro leads are for, which I would HIGHLY recommend. They're $50 on amazon. If you are not working on stuff which requires module communication to function, it's nice to have. Turn on washer fluid pumps, lights, fans, etc. Direct hook off the battery means no swapping the test light, tool does all of the work.
I have moved away from the PP3 in recent years. For instance on a power window motor, there may be a 3-wire connector instead of 2. One wire is a communications line, without which your power/ground inputs do nothing. No more unplugging and manually jumping power and ground in. I have moved more towards the old-fashioned test light, and scope use-age, followed by the meter, then Power Probe. Load-Pro leads will work on anything with banana jacks, so they do work on both scopes and basic volt meters. That said, if you are currently using jump wires as regular tools, you will be very happy with the power-probe.