Advantages and or disadvantages, sort of like life. Mylar is a type of plastic. Only owned one pair of speakers with Mylar tweeters and I too liked them. Advantages, light weight material, descent power handling, relatively cheap. Preferred the sound compared to most metal domes, but at the expensive of top end response. Tend to roll off a bit earlier, 18kHz to 20kHz compared to metal tweeters. At the time I found most metal tweeters sharp, mid 70’s speakers. Not as good as best silk domes, but this can be pricey. However there is lots to choose from in all types. If it sounds good go for it.

The only disadvantage I found was that on my tweeters wires came out of the face plate and then entered through the Mylar dome. This was not a problem until a purchased a used Phillips tuner. Europe does not use stereo indicator lights and also have a slightly higher response on FM transmissions. The tuner picked up the FM stereo indicator light as low level noise and this caused the Mylar to melt around the wire do to heat. Once eliminated the tuner no problem.

Enjoy