I used DeltaChars for a bit now, and I literally made an account just to review it because of how spectacular it is. Every piece of action in the single player campaign is outstanding, and everyone in the dialogue is written so in-character, I'm almost convinced you got Toby himself to come down and write it.
Without spoiling the experience, the new content gave me an excuse to play through the entire campaign again, and I loved the additional story added on to the game through it, along with the few little Easter Eggs I've also been able to see.
This character pack actually feels like it's a proper trio like the Fun Gang/$?$? Squad/Lancer Fan Club SHOULD be. No one character feels more powerful than the other, and using them in conjunction yields great results with the seamless on-the-fly switching mechanic. My favorite abilities of the trio have to go to Ralsei, who's great for dealing with the more annoying enemies in the game with his Pacify ability, plus his Scarf Swipe and Ember Twirl make platforming a breeze.
All in all, this is a perfect mod. It's a fun experience all the way through, and easily one of the top mods of the year in my opinion.