Helm has been replaced in practice by Vital (same author), I think.

They are completely different synths.

Vital is a wave table synth; Helm is a subtractive synth.

Helm was the first synthesizer that I really excelled with. I would recommend anyone who wants to actually learn the fundamentals of synthesis, to start on it. Once you get good at to it, it's faster to dial in the exact sound you want than to reach for a preset.

It's far more straightforward and less complicated than additive (ZynAddSubFX), FM, or wave table synths.

That being said, if you just want a very advanced synth with a lot of great presets, Vital is far more advanced.