I've done some reasonably in-depth analysis with data from RugbyPass and Super.Rugby (which is probably the closest thing to a central database - though seems a little NZ-centric) and it looks to line up very well (as they're both provided by Opta - even the match ids from each game line up).
If there was a site that deviated from these, I'd be a little more skeptical of that site - but Opta seems fairly reliable, for the most part. Some aspects of the recording may be a bit subjective, which would be my guess why other providers might offer different figures. However, the information from past games does seem to be reasonably predictive of future results (though some of my modeling is still in the very early stages). For me, I believe its very useful- though a lot of the information one might want for individual player selection isn't available on any public website I can find.