In Thracia 776, the equivalent of the Seraph Robe is the Life Ring (ライブリング Laibu no ringu), which permanently increases its user's HP by 7 when used.
In TearRing Saga: Utna Heroes Saga, the Seraph Robe's equivalent is a potion that is simply known as the Max HP Plus (MHPプラス MHP Purasu), permanently raising its user's maximum HP by 5.
If the Seraph Robe is used on the battlefield, its user's maximum HP will increase, but their current HP will not. This means that the user will need to be healed in order to take advantage of their boosted HP during the chapter they are participating in. Due to the high value of the item, it is best to either sell it or use it on a core unit. The Seraph Robe cannot be used if the user has already maximized their HP.
If a unit cannot endure 3 standard hits (or 2 standard hits, in awakening) without dying, the Seraph Robe will always be more useful than a Dracoshield. As such, Seraph Robes are best suited to units with extremely poor durability, such as Clerics, Troubadours, Thieves, particularly frail Myrmidons and mages, or units that start out massively underleveled. Dracoshields should generally be left to units that can actually expect to take 4 or more hits and keep on fighting.
On the other hand, the Seraph Robe provides a better boost than most other stat boosters, and very few units will ever be capable of maxing out the HP stat. Giving it to an overwhelmingly important unit, such a lord of the main lynchpin of one's army, could be a good idea.