Jeice is a support unit, and a very peculiar one: he not only offers 2 Ki and 20% ATK to all allies, but he also reveals the position of all enemies' Super Attacks. This is incredibly helpful is Super Battle Road, Super Attacks are the first thing that will screw your run and knowing exactly where they directed will help you in making decisions.
Jeice can be put on your Extreme STR team, he is a very good filler option: he does not link particularly well with anyone and he is not really capable of taking a hit, but he can definitely make up for that.
If put in the first slot, Jeice can also raise his allies ATK by an additional 20% for the turn, which is also the reason why the best investment for him in the Potential System is a good blend of Dodges and Additionals.
Should I run him on my team? Yes, especially if you don't have [Growing Through Battle] Hit, the best support unit for Extreme STR, you should consider using him.