Balmar generally makes good stuff, but the reviews on their newer battery monitors have been
rather mixed.. If you are looking for a stand alone battery monitor and don't plan on adding solar charge controllers, inverters etc, then the SG205 is probably a reasonable choice. But if you are also looking at other components, then the Victron smart shunt is probably better as it integrates well into to their ecosystem. Functionally they appear to be about the same.
Their old smart gauge worked very well for lead acid battery banks, but wouldn't work at all for lithium batteries.