Don't know about the big flashback arresters you are asking about. Most flashback arresters have a sintered metal filter that will quench a flame that reaches it. Note that flashback arresters are not the same as check valves. Check valves just prevent the flow of gas from one cylinder to the other, another dangerous situation. A flashback will go right through a check valve if it isn't also designed as a flashback arrester.
Some manufacturers' torches have one or both in the handle. You still need them at the bottles.
A flashback is nothing more than the flame burning inside the torch or hose. The occurence of a flashback is easy to identify. The flame at the tip of your torch is gone and you hear a high pitched squeal indicating the flame is burning inside your torch. Under some circumstances it can progress back to the bottles. But, generally, no significant damage will occur if you shut down promptly.
With a backfire, the flame burns back inside the tip, detonates and goes out. Under some circumstances it can damage the torch, send the tip flying, etc. But, generally, you just have to relight.