Is an attunement slot worth an invocation?

[Crgaston]

I have a F1/ Fey Bladelock 8 who currently has Improved Pact Weapon.

If I manage to find a magic melee weapon, would it be worth dropping IPW and using an attunement slot for a Ruby of the War Mage? The replacement invocation would probably be Agonizing Blast which would make up for no longer being able to conjure a Pact longbow, but I plan to take that next level anyway and am wondering what else might be worth it, so I guess my real question is...

What other invocations have you been able to have fun with outside of the usual recommendations? Feylocks get Greater Invisibility so the Darkness/DS combo is considerably less attractive than it might otherwise be.

And also, is it worth trading 1/3 of a resource for 1/5 of a different one?

Current invocations are Repelling Blast, IPW, Thirsting Blade and Gift of the Depths.

Any suggestions or insight would be much appreciated.

[Kane0]

It really depends on how common and powerful attunement items you come across are.

The good news is that you can swap out the invocation at a level up if you happen to come across a good weapon (regular + weapons don't use attunement by the way).

[Keravath]

1) An attunement slot is a very valuable quantity if you consider the magic items that can be used. If you have a free slot right now it doesn't matter much but down the road there could be a lot of magic items that would be more useful than a red ruby of the war mage.

2) I am guessing that you use a one handed weapon and a shield since otherwise you don't need the ability to use your weapon as a focus.

3) To cast spells with somatic components while wielding a weapon and shield you also need the War Caster feat.

However, if you are using a two handed weapon, you only need to hold it with two hands when actually attacking. When not attacking you can hold it with one hand and you have the other hand free to both manipulate material components and execute the somatic components of the spell.

So ... if you are sword and board you need warcaster and a weapon as a focus to cast spells with S,M components while holding the weapon and shield. If you are wielding a two handed weapon you need neither.

As for invocations there are a lot of good ones depending on your character's skills and inclinations. Mask of many faces is a great role playing invocation. Some of the invocations from Xanathar's are also pretty cool.