online has a different workflow, no forms mode is the main difference, and you can only do 1 return so if you want to do multiple for whatever reason or use the s/w for estimates later in the year, you can't do that with online. it generally costs more also, tho that should not apply under this offer.
heads up that desktop is delayed rolling out interview mode for some of the major sections (1099R, 1099B, Schedule A), there will be a lot of updates coming to the s/w over the next few weeks.
