Mostafa - my location is my business thanks very much!
I don't have a 'problem' with the Army - I served alongside it in various theatres in my military days and have enormous respect for it, but I do have concerns about how the Army is adapting in areas to the 21st century.
I think you vastly over estimate the scale of the challenge - at best you'll see a small number of people take up the flexible working - and I suspect those who do will either be gone for a short period (e.g. a few months) or miss the odd day per week. In coping with it, it would be like any other short term detachment for operational duty, or someone going on leave. Its just a period of absence which you wont be paid for - which I suspect will stop a lot of people from doing it.
Don't forget that its not going to be automatically granted, and that it can be turned off at any point. What I suspect will happen is that you'll see it applied for by people in certain phases of their life, and not whole platoons signing off en masse to work a 3 day week. The problem is the breathlessly sensational way this is reported, as if half the SAS will tomorrow stop working for 2 days per week.
I suspect too that an element of 'punchy fun stuff' will keep people motivated to stay in, and that those in deployable units will not want to take too much time off for fear of missing out on operations. I suspect many of those who take it up will be in Office roles. Its a simple matter though of stating that flexibility doesnt apply to units held at certain levels of readiness - after all, when was the last time we deployed Bns en masse at 24hrs notice?