Redline is way cooler !!!!
It is as simple as what care_bear has said, however, I do not believe the standard Axe board is Millennium Compliant - I may be wrong but I know that earlier in the year Lump wanted to borrow a Redline for Campaign Cup.
The other advantage of the Redline is you can customize your own settings and store these but with the standard grip you have one stored lot of settings, and if you take the battery off and leave for more than 30 seconds then this resets to standard and you need to redo your settings.
I have 3 Axe's and one has the redline as standard as its the XSV model, another I have upgraded with the Redline and the other one I have been uuming and arghing about either upgrading to the Redline or to a shockwave board.
Dont get me wrong, the standard board and gun are great, we have 15 altogether in the team and only 7 have the redline, and yet all the guns keep up with each other.
The real question is, Are you a big enough Tart to want more Paintball shiney things ???? If yes then buy one !!