The other skills like invite, almost never work. Their ability is terrible, they cause slight status changes that don't do much unless they are done many times. Their best attribute is that they can equip guns. You will also want to make sure your Summoner has a very high level of MP, even at the cost of hp, because the summons eat up tons of MP, but the summon ability is worth it.
You will want to keep you summoner throughout the game, because the summon abilities cost a lot of AP. Their summon ability is great, it can cause very high attacks, status changes and recover HP. Lancers can become extremely deadly if the build up a long versatile jumping range. Their jump ability is good, but sometimes it takes too long for them to come down. The spears have an attack range of two, and are very powerful. You have to spend a lot of time getting abilities that can work on a lot of ground, then when you do get them, the attacks only take away 10 to 60 hp at any point in the game!! Don't keep geomancers in your party any longer then you have to. They have all right attacks, and normal defense that you get with light armor. Geomancers are only good for one thing, getting other jobs.
