There seems to be a growing movement away from the traditional hydration pack/bladder combination and towards the now well established world of hydration vests. I was at first skeptical that something which hugged my body so closely could possibly be comfortable to walk in let alone to run but I've been pleasantly surprised and don't know if I'll ever be able to go back now! I first started looking for an alternative to my 18L mountain biking pack which has doubled as my adventure racing pack when I started running longer distances and needed to carry some essential survival gear as well as water and nutrition. My 18L was far too big for just running and although comfortable to walk and bike in, had a tendency to bounce around too much when I ran in it. I began looking for a pack that would instead be super comfortable for trail running but still offer me the flexibility to carry enough for day hikes in the mountains.
Enter the Osprey Dyna 1.5. I tried various vests on in the beginning and the reason I went with this option was largely down to the fact that it fit my body the best whilst still giving me all the packing flexibility that I needed. I think that finding the right vest, especially for women, is not dissimilar to bra shopping and not every pack is going to suit every body shape! The other selling points for me were the stretchy side pockets at the back (easy to stuff all sorts of odd shaped items into), the easy adjustability across the chest and the quality of the hydration bladder that comes with it. I've used Hydraulics bladders before and I've found they last well, come apart easily to clean and have generally good quality bite valves.
When I first got it home and loaded it up with gear it felt a bit weird having it sitting so snuggly against my chest and certain objects in the front pockets just didn't work in the general boob area. I later streamlined my kit to fit perfectly in the various front and back pockets but this took a couple of runs to get right. In the end I could fit the bladder with 1.5L of water, an ultralight rain jacket in one back mesh pocket, hat and gloves in the other mesh pocket, first aid supplies and survival blanket in the main back pocket, three gels and a small squeezy flask on one front pocket and another snack bar and my phone in the other. I did manage to squeeze a thin mid layer into the mix when necessary by stuffing the hat and gloves into the main pocket on the back but this was a pretty tight fit.
If you're looking for a serious ultra running vest then I don't think that the Dyna 1.5 has enough storage capacity for all of your compulsory gear plus nutrition. For shorter trail runs and marathons though I found it was just big enough with my ultra light gear. I found that the webbing at the side of the vest under my arm had a sharp edge to it which caused some chaffing on a few of my longer runs. I had to make sure it was tucked completely out of the way after I tightened it but I could still easily cut it or melt the edge smooth if I wanted to. There is also nowhere to stow your trekking poles if you're using these which was a bit of a shame as I would have preferred to have that option on some of my training runs. The mesh on the inside of the vest is really comfortable and felt a million times better than traditional packs I've run in. Overall I would recommend this to anyone who finds the fit suits them and has a small, very packable hard shell already. If your compulsory gear is a bit chunkier, you won't fit it all in this vest unfortunately.