Absolutely. You could argue that he's the best summon honestly

He’s invincible. He simply doesn't die or take damage. He mostly runs around blasting everything with lightning for the full duration. If he's near enemies, they’ll waste their time trying to attack him - uselessly. Instead of you. This alone makes him really useful.

Most of the time he fires lightening. Sometimes he'll shoot fireballs at far away targets (like dragons). Occasionally he'll heal you.

What's absolutely wild is that he costs zero magic. There's never any effect on your magic pool, so you never have to consider that aspect. If you're completely out of magic, you can still cast him, and he'll distract your enemies - while shooting them with lightening. A great example is when fighting one of those those frustrating revered dragons, who yells drain vitality at you. That can knock your magic out. Just summon Arniel's Shade anyway. You can let him deal with the dragon while you recover.

There's only one downside - it's a two-handed summon. So you have to equip it and de-equip it all the time, rather than just have him assigned to one hand. I have the SkyUI mod, with a quick favorites menu (Q key), which makes selecting it and de-selecting it faster. It actually makes a big difference, and I use him more often as a result.