In reply to Exile:
I did the 5:2 thing for about two months and lost almost a stone (I'm 6ft and went from 13.5st to almost 12.5st). I lost a lot of fat and a bit of muscle. My climbing grades improved rapidly as a result (before a shoulder injury recurrence). I have since then done the odd day of fasting as it does actually make me feel better.
I didn't do the eating window thing - just "fasted" (ie. less than 600 calories) from going to bed one night to getting up two days later. I found that, to avoid felling like death the next day, I had to consume all my calories in the evening (and have some sugar!),
I know a lot of people who have tried it and failed (to stick to it). It does take real discipline. It's hard if you have an active social and/or sporting life. I would question whether you can do it realistically if you are running 3 times a week and climbing 4x. Finding two days a week to fast is going to be hard for you I think. Whilst I did the 5:2 thing I did drop my normal exercise level a little as I thought the weight loss was worth it as a temporary measure. I did a couple of days during the week and left the weekend free to do whatever I wanted (eating/drinking/exercising).
It is hard to exercise actively on a fasting day (climb, yes, run not really I would say). I don't run but I do gym and, if I did gym on a fasting day, I had to keep aerobic exercise low. Remember that the 600 cal limit is not net of exercise, it's your gross limit.
Worth it imho if you want to lose weight fairly fast and can stick to it. I would agree with Ava that doing say one day a week would probably have similar albeit slower results and might be worth trying as you can then flex it more easily. I haven't put the weight back on and it's taught me a few things about how my body reacts to fasting and, as I say, I do it occasionally now because it makes me feel better and probably helps maintain what I consider to be a better weight for me.