First of all bear in mind that no software is perfect at beatgridding, so you will need to do a manual check anyway.
Having said that I found that rekordbox is not very good at beatgridding. More often than other programs it will return a wrong bpm value and/or a wrong phase of the grid.
I analyze my tracks first with Keyfinder in order to find the correct key and then with Traktor to find the beatgrid and then export the analyzed data to rekordbox with Rekordbuddy. With Traktor I have much less wrong beatgrids/bpm values than with rekordbox so I definitely save time.
Nevertheless also traktor gets wrong bpm/beatgrid occasionally so I always check all the analyzed tracks with the metronome and adjust them if necessary. If you are beatgridding electronic music be more suspicious if the bpm is not a round value, that could be a good sign of wrong bpm detection (with Traktor is almost always correct but with rb I find it's more common to get wrong bpm).