I use Nerdseq on a daily basis.
I had Hermod, but I did not really went deep into it so I can’t compare.
Nerseq is clearly extremely powerful.
Everything appears very clearly on the big screen and is very logical, so I did not find it difficult to learn (but of course it’s so heavily feature packed that there is definitely a learning curve for advanced features).
One of the main thing about Nerseq is that you can add expander later if you need.
I have a Nerdseq with a CV expander, a gate expander and a video expander.
All in all it gives 20 trigger outs, 26 CV outs.
It is still possible to add one more expander in case that you not be enough 
Of course the expanders are additional costs. But in a way, it’s not that expensive, because it basically gives full featured envelopes and LFOs, which otherwise would require other expensive modules.
The video expander allows sequencing directly from a computer keyboard. And connecting an external screen.
The integration with launchpad is also an interesting feature, one can connect an old launchpad and mute track, or sequence triggers from the launchpad. I use an old launchpad and I enjoy this feature a lot.
Nerdseq also has samples tracks. I never use those so I can’t comment deeper.
Nerdseq is my main sequencer, and, to me, it’s really a great sequencer.
I sometimes used it together with an Octatrack, but the interaction that I implement between both is limited. It is possible to record OT’s midi track into Nerdseq. It works great.
There’s one important thing that one needs to understand though: as a midi recorder, Nerdseq records stepped midi. So one can’t really record continuous signals (so let’s say it will no work well if you try to record a midi LFO from the OT into Nerdseq).
If you really want to sequence from the octatrack and send signals to your modular another midi to cv would probably be better. I use a polyend poly to sequence the modular from the OT and I’m very happy about the combo.
Feel free to ask technical questions about Nerdseq if you like, I’m a Nerdeq Nerd 