Hi there. I own both sets of speakers (although my MAs are the original B2s) and have done quite a bit of comparison between the two. Both are incredibly capable speakers for the money and the choice is very much down to your own personal preferences and the equipment you are using.
The 902is are very exciting speakers to listen to, with razor sharp rhythmic abilities and great drive. They can occasionally sound a bit shrill at the top end and are not necessarily always accurate tonally, but they are brilliant at what they do.
The MAs focus much more on tonal qualities, sounding much warmer but with perhaps not quite the same pace (though they are by no means slow sounding). I'd say that, overall, they are slightly better balanced than the MS 902is and worth the extra £50 but it is very much down to individual preference. Both products are very well built, with the MAs having a slight edge in terms of finish.