.. doesn't work!

My character has a device, an Illithid Mind-Blanking Device, which casts Lesser Mind Blank. Having used over half the charges, the spell has never worked on my character or another character.

It shows a visual effect on use, but doesn't do anything else.

It most likely works, you must not know what the spell does.

It lowers their intelligence d4. It won't really show more than a visual effect.

Lesser Mind Blank != Feeblemind

The later, what you're thinking of, lowers intelligence. The former grants an effect similiar to the Spell Clarity.

This item functions. At least most of them do. And they function correctly as per the mind blank the spell. -Tested-

I have a related question-

Isn't clarity or mindblank totally useless with EFU's ridiculous super-mega-duper overpowered PfE if you know in advance that you're up against EV0L?

Clarity is for cases you are fighting people of varying alignments, or you don't know what alignment they are. Like in PVP.

Clarity helps against some spells that PfE does not help against, even if you've got the right alignment.

Clarity dispells mind affecting spells. If you have been stripped from your PFA and held by a spell, Clarity fixes that.

Clarity's duration is 1 turn,

Lesser Mind Blank is 1turn/level and affects every friendly person nearby.

Lesser Mind Blank effects only you.

Mindblank is an area effect.

Clarity and Mindblank both have purposes on efu that exceed the basic PfE/PfG.

Although, due to the costs, PfA is a much cheaper source to get around most of your mental pounding if you know ahead of time what their alignment is.