Anybody recommend Henry Jekyll & Hyde?

Jekyll is fun but requires a bit of setup if you really want him to excel. What you really want with Jekyll is overcharge so he gets more value out of his buster cards when he transforms into Hyde. This is difficult without the Demonic Boudivista CE, and then a Waver to grant him the additional 50% NP charge for a turn 1 Hyde. Add that to the monstrous values he gets out of skills after transforming, Hyde becomes a DPS monster.

Outside of this setup, you're usually better off with nearly any other Berserker by virtue of having a damaging NP. The value out of his buster cards simply doesn't match up against berserkers like Lu Bu or Kiyohime unless you get Jekyll to high overcharge levels.

Imo, jekyll is just a novelty. He is a weak assassin and a fragile berserker. Summer rerun with scathach gives you a much better assassin. After that is an event with a welfare berserker, though I don't know how good paul is.

I'd say that if you have fun with him and like him, it's worth to invest in him.

Personally I don't use mine too often but I have lots of fun when I do.
The thing with him is that he's quite some trouble to make him work mostly because, as someone mentioned above, you want to make use of his overcharge, so you're usually better off just building a team around some berserker like Ibaraki as you mention.

From a gameplay perspective, he's pretty decent when it comes to skills. All of them scale well and are very consistent, and are really useful, too. He's not exactly fragile given he has a huge HP pool as Hyde and also completely heals himself when transforming.
Still, given that we have Merlin now, you can keep him alive with not so much trouble, feed him stars and also increase his already high damage on his buster cards, so, while it's quite the trouble, he still works and also might have better chances with break bars now, since you can't really nuke anymore.

You need to invest quite a bit with skills at least 666 and a powerful support like merlin with 2030. His real advantage is the second life gained by transforming, so use him on rider/mixed nodes and transform him for the last fight.

It's best to view Jekyll as a berserker rather than assassin since his performance as an assassin is too bad while he's very good in berserker-mode.

If you wanna raise an assassin you should take into consideration fighting high HP rider enemies such as the annoying, crit-spamming, AoE large dragon. In that case, it's better to raise lower stars like the Hassans since they have a damage NP, and they consume lesser resources.

If you fully invest on him he can be really good, put some grail, max his skill, get him to np 5 and try to roll demonic bodhisatva for him and you got yourself 2 servant in one body so if he's about to die just pop his np and let the berserker come to play but it is a heavy investment and even he has a ton of health as a berserker he still going to be a glass cannon so some times just easier to roll for other assassin

Np5 Jekyll with Devilish Bodhisattva is a LOT of fun.

But definitely definitely gimmicky and requires some support. Merlin feels kind of wasted on him since you don’t need the NP charge.

I think he works best as a solo servant against AOE monsters. There’s a video of Hyde soloing a demon pillar.

But he’s not particularly useful for Shinjuku, specifically.

Not using Jekyll myself. Maybe Fuuma or Serenity would be better alternatives for you?