IMO, I don't think you need to spend $$ on any tool.
About 6 month's ago, I think it was Czeck who simply said that if you measure back from the swingarm center to the center of the axle, and make those two measurements (1 on each side) as close to the same as possible, and have the chain tensioned properly at the same time, you should be fine. This method has worked for years and is very good.
Method 2: IF (and that's a big IF) your original adjustment bolts were properly done prior to your checking (like when the bike was new from factory) you can count the turns of the bolts. I usually take a magic marker and put a dot on one of the flats of the hex, then I count revolutions to loosen them so there is slack (If I were changing the sprocket(S)) and then count back when doing the final adjustments. This assumes that they were correctly adjusted to begin with AND that you can count!! hehehe. Otherwise, if you are simply adjusting the chain and it was OK before, but now just needs adjusting, then just tighten each side the exact number of turns 'till chain tension is back into spec.
"The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers