I still think they're pretty fun to use. I just recently started a new game and I'm enjoying using them.

As for my records I don't know at present. I can reach 150 with Quezacotl, Ifrit and Shiva. Not summoned Siren yet and obviously I can't do Diablos. I'll update when I've got some of the longer summons and tell you what the highest I can manage is.