The Bottom Line: The Ultimate Direction Jurek FKT Vest is a good choice for long distance road and trail runners who need to carry a small amount of food, water, and layers. The vest is very lightweight, breathable, and comfortable when running. The included bottles work, but the "kicker caps" (only found on the older bottles) are annoying and difficult to use. The vest has enough space and pockets for a day's water and food plus a lightweight extra layer.
The Jurek FKT is a popular ultralight running vest for mid- to long-distance trail and road running. I mostly use it for long runs when I want to carry water. It's so light and comfortable that I hardly notice it. The bottle pockets are on the chest, which makes a lot of difference in the balance and comfort. The waist is adjustable, though it's not easy to do on the fly. Of course, the two chest straps are also adjustable. The vest itself is a bit stretchy, which means that your range of motion is not limited at all.
The Jurek FKT has just under 12 liters of space plus an elastic compression strap on the rear that could hold a jacket or shoes or another small item. There are two pockets on the back, one larger one with a longer zipper and one smaller one. The chest straps have several pockets as well. There is one large pocket on each strap for the bottle, and there is a small elastic pocket in front where you can fit a small phone or some snacks. The left strap also has a small zippered pocket. One of my complaints is that I wish there were a better place to put my phone on the front.
This vest would be ideal for longer supported runs, with support at every 10 to 15 miles, or for one day medium-length runs. Multi-day hikes or runs are probably not an option with this vest because there is just not enough storage space. But, depending on how many extra clothes you need to carry and how much food and water you take, you could likely use this vest for a full day hike. Usually I use the vest for long runs of between 15 and 50 miles. I typically carry two 600 milliliter bottles of fluids plus an extra layer of clothing and some food; the vest still has plenty of space for a 2-liter hydration bladder.
One nice thing about the vest is that it is very breathable. I get slightly warmer when wearing the vest, but not significantly. If you have a jacket or something stuffed into the back pocket, it will likely get wet and sweaty from being next to your back. I don't think there's a way to solve this problem without sacrificing breathability, but it's something to be aware of.
The bottles included with the vest are okay. They definitely don't leak - but it's very difficult to get water out of them. Ultimate Direction has since changed their design, but the earlier bottles had a "kicker cap" (as they called it) that you had to pull and bite the rubber nozzle to drink from, but they didn't work very well. It's too hard to drink from the nozzle, so now I just unscrew the lid to drink instead. The positioning of the bottle pockets is pretty good: If the bottles swell up from pressure (like if you put carbonated soda into them and don't deflate them), then they will dig into your chest. Otherwise, they are convenient and comfortable - much more so than a "traditional" hydration bladder on your back.
Speaking of which - you can put a bladder in the back pocket as well. There are tube routes over and under the arm on both sides. There are also trekking pole holders on the front for convenience.
At around $140, the Jurek FKT is expensive for such a small pack. However, when you compare it to other lightweight vests and skins similar in weight and capacity, it competes pretty well. In my opinion, it's a good choice if you need to bring water with you but don't like running with a backpack. It's lighter, more breathable, and far more comfortable.