To furtherly expand on what I said before and avoid misunderstanding.
Alluvion sets can be augmented through special stones. Each Alluvion item has three "slots", each augmented separately with a different type of stone. "Snow-", "Leaf-" and "Dusk-" stones.
Furtherly there are 4 different sub types of stones (-tip, -slit, -dim, -orb) focusing on different augments for melee, ranged, magic and pets.
Can see a full list
here.
What makes Ttelchine items so great is that in the third slot, hence using "Duskdim" stones, one of the possible augment you can get is "Enhancing Magic Duration +", ranging from 1 to 10. Those numbers are actually % and they stack, up to a maximum of 50%.
Telchine body has a further stat (which is a basic stat, not an augment) of enhancing the DURATION of Regen (and just regen, not other enhancing magic).
There are several other items boosting Regen for SCH, some boosting potency: Bolelabunga, Bookworm Cape (augment), Arbatel Bonnet +1
and duration: Coeus, Telchine Body, Lugh's Cape
tl;dr
Telchine is good for SCH and mage jobs in general because it allows you to get up to 50% more enhancing magic duration through Duskdim Stones.
Telchine body in particular is even better because it has an additional duration boost (base stat) specific to the regen category spells.
I still think an enhancing magic duration set, while very very useful, should be considered sort of an "icing on the cake" (and what an icing it is!).
I mean, I would focus first on getting other more important pieces before you spend gazilions on Duskdim stones trying to get the right augments on Telchine items, but that's up to your personal choice I guess.
If you want a priority of Telchine Items to augment here's the order:
1) Body
2) Legs
3) Feet/Head
4) Hands
The reasons for this order: Body is the best, it doesn't conflict with other pieces and it also provides further bonus to regen. Legs do not conflict with other midcast pieces. Head/Feet are nice but head conflicts with Arbatel Bonnet for Regen (you have to choose wether you want Regen potency from Bonnet or Duration from Telchine) and Feet conflict with Academic Loafers +1 for Stormsurge augmentation during Stormspells (which arguably matters only for Ice/Dark weather tbf)
Hands conflict with Arbatel Hands+1, which is always gonna be your choice if you're using perpetuance, so they come on bottom of the list when it's about priority on what-to-augment-first.
Hope that helped you a bit on your adventures ;)