Question: How bad is Fiend of Corruption (FF) for my game?

[RedWarlock]

I've got a player wanting to use the Fiend of Corruption PrC for a character. He specifically asked for a tweaked half-fiend (half-succubus) to get there.

Modified Half-Fiend:

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Str +2, Dex +2, Int +4, and Cha +8
Outsider (native, evil): As per outsider type, Half-Succubi are proficient with all simple and martial weapons. As native outsiders, they can be raised, reincarnated, or resurrected just as other living creatures can be, and they need to eat and sleep. As per evil subtype, Allurin can have any alignment, but regardless of their individual alignment they are affected by spells and effects that depend on alignment as if they were evil. They also suffer effects according to their actual alignment. They overcome damage reduction as if their natural weapons and any weapons they wield were evil-aligned.
Medium size
Lose Spell Resistance, gain delicious kiss.
Delicious Kiss (Su): A half-succubus may use this ability when kissing a victim, or during any other act of passion. If the target is not willing to be kissed, the half-succubus must start a grapple, which provokes an attack of opportunity. The victim is dazed for 1 round, and the half-succubus is treated as though she has just consumed a good meal. The victim feels as though the experience was highly pleasurable, but is not under any supernatural compulsion to allow another kiss.
Spell like Ability Changes:
detect good 3/day instead of darkness 3/day
poison 1/day instead of desecrate 1/day
deceptive veil* at will (see below) instead of unholy blight 1/day
charm monster 1/day instead of poison 3/day
Deceptive Veil (Su): As per the spell disguise self, save that the half-succubus can appear to be up to one size smaller.
LA +4

I just want to see if anyone knows of any major problems or pitfalls with using it. The rest of the group are not really optimization-types.

Right now he's playing a Marshal 6. (I've already told him that Diplomancy won't work, though I've not yet had to prove how.)

Everything non-setting WotC-produced 3.5e and Eberron in books is allowed, as well as limited Dragon and Wizards.com material at my permission.

If the FoC is too problematic, I've told him I may just say no on the PrC, but that I'd check first.

[Nunkuruji]

Fiend's Favor can effectively buff an ally continuously.
Free Fiendish Graft for an ally each month.
Major Creation supplies poison each day, or fake materials to a merchant.
Grant Wish is only a problem if acquired before ECL17. It is certainly expected to be in play by that level.

The real problem that may arise is your PC deciding they should spam charm/suggestion/dominate/geas/etc and expect to have a legion of followers, and how you handle that as a DM.