Right, they are not all created equal, but so far of all the different ones I've seen and used, they are all interchangeable.
There isn't much to them, actually. It's a plastic shell that has two fast-on type wire connectors inside, either male or female. Those parts are what is critical, the plastic shell just holds them all together and in the proper general location. They don't need to be exact, since both ends are designed to have a bit of play in them. Basically, it's just a protected/covered set of fast-on connectors that are polarized and have a latching tab to hold them together. The design is not as critical as a coaxial cable connector.
I've had good luck with most of the different ones I've tried, including a bunch of unassembled connector only packages I picked up at a ham radio flea market. They are easy to install on your own wire. Doing it that way allows you to run custom lengths of cable and installing the connector after you have it installed. It makes some installations a lot easier.