Anyone used Open Tax Solver to do your taxes? (US)

I'd been vaguely aware of campaigns by tax-prep companies to stop the IRS from offering its own tax-prep software. I was going over some of my old tax info today, and started to wonder if there were any open source tax-prep programs.

What I found was Open Tax Solver. I get the impression that it's more clunky that using commercial tax-prep. Does anyone here have firsthand experience with it?