Garvall is a very powerful Dark magic damage dealer that excels in short fights, as well as provides a valuable TMR for mages in general.
With the release of Garvall comes the new job: Energist. A job that gives high damage (Twin Chi Rupture), good range, no cast time, and one skill that has 100% hit chance (Detonation Blast), all at the cost of some fairly high AP. Paired this with the high MAG stat that he can get from the passives (Hyper-Vitality + MAG Up Lv. 1), and some spirit penetration from Limit Burst (or magic resistance penetration from his TMR), makes him quite the powerhouse. Despite all of that, he's not really a glass cannon since he comes with the skill that reduces 3 physical damage taken by up to 50% (Chi Barrier), and 2 attack type resistances by 10% at base.
His other subjobs being Kotodama Wielder and Red Mage adds more to his focused MAG stat, but they might not add much in terms of skills, especially since most of them have cast time which can end up slowing him down. Kotodama Wielder has some useful skills to help with mobility, and a good general counter skill, while Red Mage gives him access to situationally useful spells and Jamming Thrust.
It's worth noting that he has -10% resistance to magic despite being a magic user, though he has a passive to increase this. You will want to be careful when going against Light magic enemies, or units like Sakura in PvP.
Unless you already have several strong dark magic damage dealers, Garvall is definitely worth pulling for. He's a good unit to use in general, whether it's farming/grinding or PvP. The JP server shows that he's still strong and relevant a few months later down the line in a EX job era, despite not having one (yet).