In theory I would agree, if the circuit can be maintained while achieving accessible, accurate, reliable, detailed resolution without wandering results then great, what more do you need...
I have not yet tested the fuse method, but have had a look at a few cars, and especially on Mini fuses we have a high proportion with no access point in the plastic to be able to probe for a reading, so the circuit will need to get broken in any event. ;-(
We will do some tests using sample fuses from real cars of various amperage using a known current load (probably 50ma, 500ma and 5amp) to see the consistency of the readings of the fuses and how much variation there is, including time to see if heat has any impact. Subject to this all being ok, then my quest is almost complete ...
so going back to my original goal, to measure parasitic drain over extended periods, we can adapt a fuse/holder, to provide easy 4mm banana lead access, to bridge the earth cable and allow testing without ever loosing memory of the car, and if we can achieve the resolution needed, 5-10ma detail, then using a 20-30amp fuse will mean we can trigger using door locking without fear! (I guess using a proper suitable Resistor to do this might be even better, anyone got an RS Part number?!)
However having an inline testing tool with impressive resolution, in the tool box, would be very handy, firstly you'd save a channel on the scope, which might be important, second the resolution and accuracy may end up being far better. I like options, and not having any inline device I can use with Pico is a gap I'd like to fill (though it might be used a lot less than I think if all goes well)!
I'm really impressed with the forums here, having people share/come up with solutions that I would never have found on my own, due to blinkered approach more than anything, I should have shared these issues years ago!
I guess some testing, prove the accuracy and reliability of the fuse method, and maybe checking all the fuses we buy have the ability to be probed! In Jan we'll do some tests, build some maths channels and post some results here.
Thanks for all the input and help, wishing you all a great Holiday Season and for to a Prosperous Year to come!