First of all, I like it the idea to have a single instrument to tweak harmonics. And I think Harmonic Bloom is a really useful and beautiful plugin to work with.
I like the sound of the waves and the noisy samples that come with the plugin. I like the simplicity of the GUI and the beauty of its skin.
It may be possible to create such an instrument with common synth plugins somehow, but what makes this plugin outstanding is that it offers several modulation sources for every single fundamental and seven of its harmonics in one environment.
It took me a second to understand (this was the only time I looked into the manual), that the LFOs have negative and positive values (which is great) and that therefore the mod knobs all the way down to the left means not zero but fully negative value. But when I got this I loved to work with it.
There is an objection finally: Harmonics is something one adds to a soundscape, it's not a basic tool in my opinion. I understand that the company is not a big player like NI, or Arturia, or u-he, you name it. And yes, the samples are really numerous and useful. But in the end, the users pay for of a plugin that 'just' adds things and may ask if it's worth buying it for 145,-$ (I got it 24% off on KVR Market place). To be honest, I found the plugin too expensive, therefore I give 4 stars.