Peter Parry wrote:

Most manufacturers say their purpose is for "behaviour modification"
rather than measurement. Whether the "modification" is worthwhile
doesn't seem to be considered to be particularly important.

Was for me. I got one from work to test (at the time it was a prototype
not yet on general sale), and having a consumption figure on the wall
(whether precisely accurate or not) stopped my lodgers leaving all the
lights on all the time. Since I pay the bills (their rents are
all-inclusive) that's a win as far as I'm concerned :-)

Pete