Hydration Vests?

I am going to need a hydration vest for this half marathon training out in the summer heat (which we are FINALLY getting a glimpse of). I saw a great review on Katie @ Runs for Cookies about a CamelBak Marathon Hydration Vest that holds 70 oz of water. This was almost $100, & I'm not sure I need 70 oz. Granted, it is the one I like more of course. Now, if anyone else is drinking out of my pack, I may need them to bust out some $$$$ and we will do the 70. If not, I really like this one: 

Camelbak Dart holds 50 oz/1.5L for $65.00

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Do y'all have hydration vests? If so let me know what you think about them!