I haven't had bad side effects from guard mode. I have bad side effects from not using guard mode with spear using troops like hoplites. They die faster even while killing enemies faster.

I think that iphikratous hoplitai could be more useful for its cost if it was very hardy and had more defensive skill to account for the lighter kit. I'm thinking 10 or 12 instead of 8. I'm arguing only on paper so I don't know if it would make a difference in the game. I think they'd be more durable that way.