FM Synthesis Module

Can anyone knowledgeable about FM synthesis critique the capabilities of the OP-1’s FM synth?
I was watching Nick Batt’s review of the Volca FM and it got me really curious about how it all actually works/how it works on the OP-1.

You may check @raigan’s OP101 blog:

http://op-101.blogspot.fr/2011/09/fm-critique.html

Whoa, awesome. Thanks!