I had a friend lend hers to me when I was a kid, and I did in fact try it in a cassette player! I even tried to make my own cassette, but I soon realized that I couldn't because... All 4 tracks had to be recorded in the same direction.

2-XL used the left and right stereo tracks of each "side" of the tape to store four total synchronized audio tracks, but all in the same direction of play. If you listened to "side A" on a normal cassette player, you'd hear two tracks: one on the left and one on the right. If you listened to "side B" you'd hear the other two tracks, but played backwards.

You could have reversed the audio for two of the tracks before recording.

You'd also have to be very precise in laying down the reversed side, to ensure synchronization

Four track cassette recorders work this way as well. Made many band demo albums with one.

I listened to many a backward message with my old Tascam.

Before then, I used to turn over a spindle, leaving the "rolled" part of the tape outside of the guides, fast forward through the whole tape, then turn over the remaining spindle and close it back up with the tape behind the guides again. This way you were playing the tape backward, but through the back of the tape, so it was a bit muddy, but worked.

With the 4 track recorder, you just mute tracks 1 and 2, and listen to the opposite side of the tape (the side not facing you) backward.

Yea, I was a weird kid. But my best experiment from this ended up on VSauce, so there is that.