Just like Apururu, he casts haste 1, which can be annoying when you want a RDM to keep Haste2 on you instead.
This ruined Ygnas for me.
I know, right?
A "trick" you can use for that, is to use Arciela1 as your RDM of choice.
Arciela1 will always overwrite Haste1 with her Haste2 (but she casts only on the summoner).
Her priority in doing that isn't super high, but she does it.
Still pretty annoying, but it's an okaysh compromise. Plus Ygnas gets a Refresh aura if you use him with Arciela.
If Haste1 isn't an issue, I think Ygnas is a valid alternative to Yoran-Oran, allowing you to pick Sylvie as your Unity.
But if you need AoE heals, there's really no substitute for Apururu alas.
She's literally the only main-healer-trust that regularly casts curagas.
(there are other NPCs that have curaga or similar spells, but nobody is an efficient "main healer" like Apururu)