I am in Florida and use an HSM by Adams.
Heat - I can definately say that heat is not an issue. Let's face it...if it was I would know due to geography. In fact, I get less sunburn and tanning using the helmet, especially in the ears.
Weight - (this is probably one of the heaviest helmets made) but, because it distributes the weight evenly over your head, it is remarkebly comfortable.
Vision - I haven't noticed much difference between a traditional mask and the HSM
Mechanics - If you treat it like a mask, you will have no issues.
Protection - 1 thrown bat and several fouls balls to the back of the head....I'm glad I wear it. Fast ball to the face...the impact is destributed evenly to reduce impact.
Just my humble opinion but, I hope it helps.
Thanks