This saddle is an outstanding piece of kit, but there are some caveats that you need to understand. First, I've tried many different saddle brands, types, and set ups. I am an experienced rider with good flexibility. My riding style is to slide rearward on the saddle a lot but also have room at the front of the saddle in certain situations. My preference is a flat, narrow saddle with plenty of real estate, that's the Arione. If that is you, then you are on the way to choosing this saddle. Being able to slide back behind the bottom bracket, allows the most unweighting of the upper body and the most comfort on long rides. See Steve Hogg's bike fit website if you need more info.
Next, do you like the feeling of flex in your saddle when you go over bumps? I do. If so, check box number 2. This expensive carbon saddle has a superb and unique characteristic of smoothing out bumps and flexing along the sides and middle of the saddle. I have tried saddles with cut outs and this saddle is just as comfortable. It is not immediately obvious, but the Arione 00 has a very slight dip in the middle of the saddle and flexes like a hammock.
Next, do you have a decent budget for your gear and do you like well crafted stuff? If so, check box number 3. The Arione 00 is a hand made work of art. The carbon shell and shape of the rails bonded to the shell is basically like a sculpture. It looks good in your hand and great on your bike.
Weight exactly 146 grams on my digital scale.
Fizik markets this saddle for the snake, with flexible back and not much pelvic tilt. That's definitely me BUT realize that tilting the pelvis at the hip hinge is an important position that bike fitters advocate to better engage the big muscles in your legs and glutes, and I have found the Arione 00 very comfy even with that position. BUT, it is also comfy with your back more flexed and rounded and allows you to perch on the saddle rather than within it.
The bottom line is that the Arione shape is likely the most versatile saddle shape, which of course is why it is so popular. So why buy the 00 version? First, the carbon shell flexes better than the cheaper versions. Second, it is lighter than the Arione Kium, but honestly, that's not the main selling point. The most important reason is the feeling of having the best, something special. Is it worth $300? No. I paid 264. Is it worth $264? Probably not. Do I regret buying it? Not at all.
Over the years I've used 10 or so different saddles from just about all major brands without any problems so I suppose I am not particularly sensitive (physically) to saddles. Even so, the design of the Arione 00 gave me pause due to its' long nose and tapered sides (wings). I needn't have worried - after 1,500 miles since purchasing (50 to 75 miles per ride - climbing, sprints, fast pace, distance) it has proven to be the most comfortable saddle I've owned. Typically, I have applied a 0 tilt angle but with Arione 00 it seems like this isn't possible. On my saddle, the back half sits at at an almost 0 angle while the front angles downwards at about 4.4 degrees. Surprisingly, this works out quite well. I can sit up and shift backwards on the saddle for comfort, or, when going hard, the slight downward angle of the nose makes it more comfortable in the drops. The only gray area is the middle of the saddle where, on occasion, with too forward a position and riding the tops or hoods, the downward tilt puts too much pressure/weight forward but a slight shift aft and I find the sweet spot for this position. All that said, I am particularly flexible so moving around on the saddle isn't a problem. Finally, one proviso on the comfort of the saddle is that I switched shorts from a brand that rhymes with Twirl to Assos. The Assos are silly expensive but they fit amazingly and have more padding so this may be a contributing factor (or confounding variable). So far, there really is not anything that I dislike about the saddle.