RE: deFacto for Dynamics GP
The primary issues we see around MR revolve around the data mart, which you said you don't use. MS is moving that way and I expect them to retire the legacy connector at some point.
deFacto uses an analysis cube to aggregate its data. It is significantly faster than FRx or MR's legacy connector with large amounts of data. Plus you have Excel as the primary reporting tool. This eliminates exporting to Excel and reformatting.
In a number of cases, the people I see using deFacto did not have FRx or MR as an option. They simply had too much data to reasonably process through the legacy connector. deFacto handles it fine.
Mark