[Agema]

As a general rule, I find the national summons rather better than the all-access summons for the gem cost, although they aren't necessarily the best summons.

Personally I love Sea King's court. They're certainly far superior to the Earth magic landlubber troll court. The sea trolls are only mediocre fighters and weakly armoured, but their huge HP and regeneration make them hard to kill. The Sea King himself is not only a great thug, but has W3 and spawns W gems.

As I see it, you get 20 trolls easily worth a gem apiece, and the remaining 35 is a fair cost for an magic level 3 thug-quality mage, a harbinger being comparable.