ElCeejo’s post sums it up. Mobkit is less laggy than mobs_redo, and offers more mob behavior options. It works alongside mobs_redo without problem.
I would suggest installing mobkit alongside mobs_redo, and work towards converting all the way over to mobkit eventually. However there is no rush. Everything will work fine with both installed.
An immediate benefit of adding mobkit is that you can add paleotest dinos and that you can add gundul’s water_life. Water_life adds Large wales that navigate properly in the deep sea, seagulls, beavers, mosquitos, more fish, rattlesnakes that bite and need an antidote, piranhas, little lizards and more. There are some mobs from it you will want to disable, like the shark, maybe the mosquitoes.
another neat mod you can add with mobkit is zombies that are actually attracted by movement, and can only be killed by a decisive whack to the head, rather than to other parts of its body.