I used it at my former firm last year, with UltraTax (also first year using that). It was an unmitigated disaster. Far too many duplicated entries. Mind you, we got it up and running in January and got no training from UltraTax or Gruntworx. I may be wrong, but I think that may have made a difference. I gather UltraTax has a module that is intended for non-technical staff to pull in basic paperwork. My hunch is that this caused a major problem, but my former employer disagreed.
I could see this working well if you have lots of clients with hefty taxable investment portfolios. If your market is in small business owners with a K-1 and a few other bits and pieces, I remain unconvinced that Gruntworx would be a good investment.