The DA42 (G1000) fuel metering is interesting. I don't think most pilots know whether it is a gauge or a totaliser; the latter needs manual entry of the FOB figure otherwise the subsequent reading makes no sense.
Technically, both
Totalisers also need a bit of care, as you've highlighted. I'll again use Cirrus tanks as an example: it's extremely easy to fill the tanks to the brim, put the caps back on, and assume that the aircraft now has 212L useable avgas on board. Chances are it actually has less than 200L - the fuel takes a little while to settle in the tanks, so it's not uncommon for us to be able to get 5-10L more into a tank that at first glance appears full. Not really a massive amount for 2-3hr flights or training details, but potentially 20 mins extra fuel on a trip that's planned down to reserves.