Recently I've added a wavefolder to my rack to break out of traditional subtractive synthesis. I've been looking around for other types of synthesis and I stumbled upon through-zero (or thru-zero) frequency modulation. As far as I understand, through-zero FM doesn't have the pitch-shifting effect that you get when you increase the FM amount on linear or exponential FM oscillators. As far as I've also understand is that "traditional" FM sounds are typically made using sine oscillators.

This brings me to the Happy Nerding FM aid. It's advertised as "designed to perform through-zero linear Frequency Modulation (FM)". This module does not only have a sine output, but also triangle, sawtooth and square outputs. The way I interpret this module, is that with two sawtooth oscillators as inputs (according to the manual, this is what FM aid expects), I can create "traditional" FM style sounds with the FM aid when I use the sine output.

However, a lot of videos I've seen are going into the other waveform outputs of the FM aid, creating harmonically rich synched-like overtones and PWM type sounds. Happy Nerding themselves even have a video called "FM aid folds" and I've heard more videos in which someone mentioned "folded" waveshapes.

This makes me doubt if this module is designed to make tradidtional FM style sounds. Can anyone clarify this?

Also, a bit off-topic: I was assuming that an FM oscillator and a wavefolder added to an oscillator have different, distinctive sounds. Is this the case or do FM and wavefolded sound quite the same?

Thanks in advance!