The flex on the ones I have found in catalogs online, are almost all limited to 15°, so the change in length is insignificant.
As far as having a flex or rigid, it all depends on what you might use it for. I had never used one until a co-worker checked one out of the tool room at work, as all of the torque wrenches we usually use were already out. I was pleasantly surprised at how much easier the slight flex made the job we were doing, so a few weeks later when I was doing another job in a tight area, I stopped and walked past one toolroom that I knew did not have the flex head and on down to the one that did (another 900 ft or so in the other end of the building) It made a knuckle scraper of a job into a piece of cake. Not long after that, I bought a 3/8 drive and a 1/2 drive from Tooltopia. Free shipping on orders over $100, fast too, I had mine in about three days.
Charles