Speaking from some age and experience, turnbacks are only feasible if your rate of acceleration on takeoff is high (which shows as speed or height in hand) and your rate of descent low after an engine failure. These conditions do not, in general, apply to piston aircraft, so the WWII and 50's mantra was "never turn back". Early jets could turnback successfully, provided you had passed a critical point in the takeoff, and from the later stages you could actualy carry out a circuit and land into wind. Not many people did this!
I know that turnbacks were taught and practised dual in JPs, but even then, with bang seats there was little point. If in doubt, get out, and if in trouble, go through the bubble, as we used to say.
I have no knowledge of big jets, but suspect that turnbacks would be feasible. But, again, what's the point, unless all 4 (or 2 or 3) go out together?
Just for an illustration, on a certain early jet, one of our squadron had engine failure after takeoff and turned back. He arrived at the runway going far too fast, shot right across the field and into a concrete blast pen at about 100kt. Following the inevitable crunching noise a small figure appeared flying through the air, his parachute deployed and the canopy still caught in the wreckage. He reached the end of his rigging lines, dropped 10ft to the ground, unlocked his harness and walked away. He then collected his car keys and ciggies from his locker, drove home and retired by post. We never saw him again.
My advice? In a small piston or low-powered turb do not expect to be able to turn back from early EFATOs. There will be some critical point beyond which a turnback may be possible (c.f. Bulldogs), but only if you know what you are doing.
Dick W.