There have been many threads on battery State Of Charge (SOC). That is a very important value if you want to get maximum life out of your house batteries.
Almost all experts agree that you should not take your deep cycle batteries below 50% SOC (for wet batteries - a bit lower for AGM). Voltage is not an indicator of SOC unless you have no activity (charge/drain) for several hours and that just does not happen in our application. The SOC type meter (I have the Trimetric as well) gives you a pretty darn good indication of SOC since it has an integrating computer that measures the amperage flow in and out of the battery.
The main function is to report SOC. However, it has the ability to display battery voltage and current flow (shows as a minus when you are drawing from the battery). Current flow can very interesting. You can see the impact of any/all of the 12V and 120V components that operate through the inverter/battery system. I have done quite a bit of playing using the current meter by turning stuff off and on to see just how much battery draw I get for that item. Course, that is a weird engineer trait
I would recommend this kind of meter whether you have solar or not!