My bottle of 277 (red) is more than 20 years old, and still works fine. Locks up the nuts but can be readily taken apart. But as others have said, some of the threadlockers are deadly, especially if they cover an extended length of thread e.g. 20mm on a small diameter bolt will mean that you shear the bolt before the thread releases. Lots of heat is your only hope. The thin formulations can really 'wick in'. I once read a report (some problem on an aircraft) in which traces of a threadlocker were detected along a 200mm path, basically attributed to capillary action. I've got a bottle of green threadlocker somewhere (can't remember the number) that must be 15+ years old, but I very rarely use it – I generally like to have the option of taking something apart, maybe!
The activators for use with the retainer grade e.g. for fixing anodized aluminium together, can work exceedingly well – when you come to put the two pieces together you'd better get it exactly right, and fast. It can be almost like superglue.
If you haven't used it before, I'd suggest getting some of the weaker and some of the really strong grades, then do a few tests on threads that are, say, just 'wiped over' clean, and others that are truly clean (degreasers, alcohol-wiped, etc) so that you have a true appreciation of how strong they can be.
Roger