"..thinking of getting the Sinclair... Good/Bad????"
Excellant choice, get the less costly dial indicator, it's plenty good.
"Are they worth the investment for hunting loads???"
Bigger question. For normal hunting, inside maybe 300 yards, probably not. The differences may be a lot by percentage of change but we're still talking about fractions of a Minute of Angle. I'm generally satiafied with 2 MOA accuracy for deer hunting but my best .30-06 loads cut that to a bit less than half - the deer can't tell any difference tho. I mean, even at 200 yards my worst hit will be off the cross wires either by 2 inchs or a bit under 1 inch. Big deal! ??
But, Sinclair's gage is the way to go.