I used a piece of wire hanger bent at a 90 and a tiewrap cut at an angle to form a point.
I'd be damned if I was going to pay $50 for the "Special Tool"

 

Ive always done it by eye,adjust for the belt tension and then center the wheel. Spin the rear wheel and watch the belt on the sprocket and the tire in the swing arm.
Done it since 1994 on 4 HD and more than 80,000 miles and 6 new rear tires. never had a problem.

never seen any of the techs at the local dealer or indy shop use a "tool".

 

I've never watched a tech do it, so I find this interesting...

I do mine the same as you... adjust for belt tension, center the wheel, then check the alignment...

But, I use the tool when checking the alignment of my rear wheels. It's actually faster, for me, to use the tool to confirm it's centered (and make a minor adjustment if necessary)... than to spin the wheel and watch for the alignment, make an adjustment if necessary, and then re-spin the wheel... and of course, it removes the time I look at the wheel and second guess myself.....