The skills Bouncer/Braver/Phantom Mag convert your Mag's Dex stat across multiple Attack stats. Mel/Rng for Braver, Mel/Tec for Bouncer, and all three for Phantom. This makes a Dex mag viable, and my personal preference! But that's not all... These are NOT Main Class only skills. Using a combination of these as your Main/Sub will grant you 400 in your preferred stat, twice what is normally possible from your Mag.
BoBr/BrBo don't actually synergize all that well together, though it'll certainly work well enough until you get into the higher level content.
The true potential of this comes from Phantom sub. Phantom is a Successor Class in JP, though I believe they've been renamed to Scion Classes for NA. You unlock them after getting to 75 in any two normal classes. Phantom works really well as a subclass, providing technique access/buffs, extra PP, and large, consistent multipliers to damage and crit chance. And its Mag skill, as mentioned above, converts Dex into all three attack stats.
For BoPh, this means a maximum of 400 Mel, 200 Rng, and 400 Tec, which in addition to just being a great boost to your damage output, will help you equip basically whatever you want by endgame. It also allows you to use techs to much greater effect than other Bouncer builds can, thanks to the cast speed and PP buffs. Also worth noting is that Mag skills don't actually "convert" your Dex into Attack. You'll still be getting the full 200 Dex from your Mag, in addition to the attack. This means that using BoPh will give you a total of 1200 stat points from a single Mag.
TL;DR: Dex Mag best Mag