I've used my WTF stalker vest a lot lately and have to say that it is amazing. While it is cool up here in the great white north right now, I don't foresee the vest being overly hot in the summer here for 3 main reasons.
1) There is no back to the vest, it is completely open which leaves my whole back an area to vent and breath.
2) Mine has the 3D airmesh backing. It looks like it will breath well and also feels comfortable.
3)The vest portion is actually relatively small. It reminds me of a handgun (pistol) shooting vest my dad bought me as a kid. It only covers the man boob area of my chest (pectorals) and then the tubes hang down to above my belly button (navel). This also allows a great degree of freedom in terms of movement.
Since I can hold up more than 14 tubes it's versatile for any play style. Keep it fully loaded for scenarios or just bring 4 tubes for walk on games.
It has places for 12ies and your squeegee. I feel like the dudes at WTF really thought this sucker out.
And as for having the hard parts on your back vs your front I find I just don't get shot where the tubes are a lot. That area is normally kept safe behind a bunker. When I come out to shoot I don't like sticking my nipples in the wind. That's just risky. The few shots on the shoulder area/upper chest space where I have been shot have been bounces due to I believe the airmesh backing making it thicker.
Just my 2 cents. Hopefully this helps someone out. Here's some winter fun pics. Sorry if they're a bit big.