For years I had a Link something-or-other Ah counter. It worked fine, as long as all the settings are right, you return to full charge on a reasonable frequency, and you adjust the settings as the battery ages. The down side is that you tend to take the reading as gospel, and it can be quite wrong at times.
For the past 10 years, both on land and on boats, I've just used voltage and amps. It's not super precise, but close enough. You need to get a feel for how voltage sags or rises based on current, and you need to get a feel for voltage with whatever your background load level is, but that load level is typically quite small relative to the bank capacity. Mine is about 0.02C. With a little experience it works just fine.
I hear over and over again about how voltage is a poor SOC indicator unless the battery has zero load and has been resting for hours and hours. In my experience that's total hogwash. Maybe if you are running a forklift or other heavy load it would matter more, but I have consistently seen voltages recover within minutes, not hours. And if you are accurate to within a tenth of a volt or so, you will know the SOC to within 10% or so. Close enough to know whether it's time to start the generator.
And on recharge, just watch the voltage and the return current and you will know if you are fully charged.