Jinbei is maybe not the funniest character out there, but so wasn't Robin till EL.
Jinbei is light hearted as well as shown from time to time and I like his personality. On top of that I love his fighting style and the whole fishmen karate stuff and I hope it will be kept in the story.
I always thought of him joining ever since Luffy saying to him "He is amazing" but now with the flashback, Nami interaction, chapter title being called 10 vs 100,000, having a fight together with Sanji and so on, I'm completely sure that he will join.
The cons about him become more and more valid and the only one which is staying his the not seen crew. All we know is that after Jinbei took his position the ones who wanted to stay pirates created crews like Marco and Arlong… The others stopped being pirates and never wanted to be ones after all.
Now they may be wanted... BUT where are they. If they would be close shouldn't Jinbei call them helping to defend the kingdom? Yeah he should... I just think they are living somewhere else... Cuz besides Jinbei, Tiger and Arlong non of them had a bounty poster after all and no one would recognize them... Just look at Sanji... he has a bounty poster (a fucked up) and still people don't get who he is.