Ron - it would be a good test at a technical level. Zoom back out to the "system safety" level and then re-examine the value of the test.
In Canada, with 406MHz ELT's we have only recently been granted the ability to do every other annual inspection "on wing" through documenting the manufacturer's recommended ELT self-test. This self-test is predicated on the very important principle that we're not disturbing anything to do this test. That means we're not messing with the ON_OFF_ARM switch on the ELT itself, or with its mechanical retention features, and not with its wiring/connectors.
Part of the reason we have gained this little bit of relief on 406MHz ELTs in Canada is because the "on wing" inspection removes one cycle of potential Maintenance-Induced-Failure (MIF). Break open the connections to insert the data test device and now you have opened yourself up to a MIF, exactly what we have been trying to get away from.
I would highly recommend avoiding going any more deeply than a good visual inspection of all ELT components and a functional check using the self-test function in the first five minutes of the UTC hour.
Remember, if you are doing the "on wing" test this year, next year your 406MHz ELT has to go back to an Approved Maintenance Organisation for its performance test. The "on wing" test is only every other year.
