bookworm
I have a Shadin and agree that something like that helps a great deal. However I would say that without a physical check of tank content, or an accurate fuel gauge (and in the context of GA the latter should not be relied on even if you have it, particularly as the former is so easy to do) anything one does is pretty worthless.
When my plane was delivered, the Shadin was reading 25% out. After some messing about, over a few months and much calibration against the pump, I got it down to 2%. However they do fail; I am on my 3rd one now within 1 year; the current unit goes to sleep occassionally! They all have a bug which causes them to occassionally lose the FOB setting one puts in; the work-around appears to be to not switch it off too soon after setting the new FOB figure.
I find the Shadin's best feature being the accurate fuel flow RATE indication. Knowing one has say 86USG in the tank to start with, and with the Shadin showing 12GPH flow rate, there is no reason to run out. Especially as one knows what the flow rate is at a given power setting. I would NEVER entirely rely on a Shadin as a totaliser, i.e. to tell me how much is actually left in the tank.
In the context of this thread (a low hour pilot renting a self fly hire plane) I've got a feeling that neither did he know the flow rates at different power settings, nor did anyone else know, nor was there any way (due to lack of instrumentation) for him to find out. In that situation, a gross over-fill is the only way. All the debate about how much he should have put in, etc, seems to be the difference between him returning with a nearly empty tank, and him returning with a completely empty tank. Neither is very clever.
As regards other posts about solid state (capacitive) fuel gauges being expensive, they are no more expensive to make than the WW1 systems fitted to most planes presently operating. I think it is simply a matter of nobody being willing to process an STC for an item because few operators would buy it as a retrofit item. With a largely decrepit fleet, almost nobody will spend money on "non essential" items. The planes I used to fly often didn't even have working lights; the school would not spend the money unless one was doing a night rating in it.