Not calling it useless, but the situations where I think I'd want it don't feel too hot. As is, for Shellga, I can either set the ability or run with one of the WHMs who have it as a SB (with Mako Might if needed). Boon is probably more useful than this because of the Haste over the regen, similar to how Edgar might get edged out by Red. If I do need AoE healing, my first choice would likely be a Yuna RW. For the few reflect-heavy fights we've had, Kirin has also usually been enough at 2 charges.
Being a Monk, I can't really expect him to be an offensive powerhouse. As I think someone else noted earlier, he hasn't been 80 broken in JP land, either. This means he'd ultimately be a breaker, but if I'm facing difficult content, I'm probably gonna want someone who can use the BDs, anyway. Since I've got Vaan's dagger, he can do the same, but better. And if a boss is vulnerable to Sap, bonus. Mitigation is likely otherwise covered elsewhere. Pragmatically, yeah, I'd probably use him over Zidane or Steiner with IX synergy, but it's still a hard sell elsewhere.
For me it's bordering on useless for two reasons:
1. I have boon and aura doesn't really synergize with boon. If I want high regen I'll use a fabled song RW as that will give protect and high regen.
2. I've built my melee parties around celerity skills. The hastega from boon allows even my slowest celerity users to attack approximately every 3 seconds while non-celerity skill users are every around 3.45 seconds. Therefore, celerity users can get in 10 attacks before other skills have even gotten a 9th attack in.
I would really like to use them since they are my highest attack weapon but the trade off in overall damage doesn't make much sense to me.
Waterga and Waterja have 1.5 sec casting times vs. 1.8 for all the other -aga and -ajas.
You guys make some good points, and I suppose it does depend on what relics you have. I'm taking those quoted lines slightly out of context, but they are precisely my point. You're both saying that if you need AoE healing, you'd take a specific RW. That's fair, and that's actually what I do as well. I also have Boon (but no LH), so I understand the overlap. But if you had his SB available in your party to cover healing, you'd be able to take Planet Protector, SG/SSII, or other things in your RW slot.
Admittedly, that mainly works on fights where you can charge SB, like DU Elites and Boss Rushes. On the single fights, it's true that he's probably not worth your Mako Might.
Also he's a monk and monks are meh
It would only be useful if you didn't already have a Regen or haste relic. If you had LH, you'd use Aura. If you have Boon, you'd use Fabled Song.
Fought event Amarant, failed to master because I forgot to bring Zidane, do it a second time, mastered and got GFO and Garnet's RM2, makes me glad I did it second time.
Gonna do 1 100 gems and 1 15 mythrils time to fail
Planning on doing the same. We'll see who has the better luck!
Good luck, gentlemen.
May the odds ever be in your favor.
All 3* too. lol
Meh, I did 5 pulls and ended up with 2 4* diamond swords and 0 5*. Oh well, time to do the boss rush.

Pulled Golem's Flute from 100 Gem.
Was aiming for Vivi's relic, but guess I'll stop here.
Healing rod from 11 pull :/
Genji Armor from 100 gem. Game's trolling.
100 gem pull, 4* FF5 rod.
Tried 1 mythril pull. same 4* FF5 rod.
Thanks universe for slapping my wrist.
RIP 165 Mythril. Fucking game really wants me to play physical, mage weapons are a hoax.
Defender
Coral Sword
Cat's Claws
Golden Shield (FFVI, my second)
Storm Staff
And a bunch of crap to combine for various other physical weapons, sigh. I just wanted a flute -.-
What if i have all 3? To date: 3 fabled harps, 3 vega 42's, 2 diamond pins. My hones are seriously lacking though, currintly sitting at 83 2/5 stamina shards.
Just did a couple of pulls, ended up getting 2 5*'s an ice staff & dragon armlet. So nothing great, at least i have another mage staff.
Finished bonus battles
Shits too easy
Blind + fire + holy reks soulcage