My first set went haywire, second set is still ok but most are under $20 bucks so no dramas really. I got the more sensitive ...up to 30 grams model to two dec points and a calibration weight.
The only issue I have had, works great on the alluvial "less than a gram stuff", but when I wanted to weigh a 100 carat stone (about 35grams) it could not, and to do a specific gravity test one also needs a bigger scale.
Id suggest 2 scales, a sensitive one for the sub gram stuff, and a general larger one in case you find a speci and need to do an SG test with water, cup and string.
I'm always dubious of the scales that indicate they measure big and small stuff.....Maybe someone has a scale that does both scenarios ok.....?? You don't want to be putting a .77g nugget on a scale and it reads 1gram if you know what I mean.