If I already had all the shards needed for a matrix cube and was broke when I hit 50, then I would probably use a cube until I could buy the DG relics. But personally, those shards can be a real pain in the ***** and I would rather spend the 11k.

As a fresh 50, the difference between a matrix cube and BM relic is probably not that big of a deal when running entry level endgame content. To each his own.