Hello! Thanks for reading and for the interesting question!
I like the WS1100iS. I think they’re an underrated pair of headphones with a silly name. The MSR7 gets most of the spotlight for being the “Neutral” pair, but I think the 1100iS is just as viable a product.
It only has a couple of drawbacks compared to the HRM-6, and they might not be drawbacks depending on your use case.
Sound-wise, the WS1100is is a brighter headphone. It has slightly cleaner, slightly more present highs. That’s just the Audio-Technica way, haha. If you’ve used other AT headphones and enjoyed their particular character, you’d probably like the sound of the 1100’s.
The biggest potential pitfall is that the 1100iS is semi-open. It’s perhaps the only headphone I’ve used in that category that I think truly deserves that name. Most semi-open headphones I’ve used have been more or less fully open…but not the 1100iS.
It has an amount of isolation squarely between closed and open-backed models, and a bit of sound leak as well. The HRM-6’s also leak a bit through their ports, as I mentioned in the above showdown…but ports are pretty common in closed-backed headphones and don’t ever leak quite as much as the 1100iS does.
Even the DT770, which isolates excellently, has small bass reflex ports on the back.
If the ports aren’t an issue, then the ear pad size might be. The 1100’s have much larger openings in their pads, which could be a blessing or a curse. I think the HRM-6 pads are plenty big for just about any ear size, and the 1100’s might be too big to seal around your ear correctly. I managed it alright, but I’ve had issues with other large pads sealing in the past.
The 1100’s feel a little lighter in the build department…but I think they’re built about as well as the HRM-6’s. Both of them have similar styling and touches of metal. The 1100’s don’t fold down though.
So in summary: They’re very similar headphones. The 1100iS is more open, a little brighter in sound, and doesn’t fold down.
If you can find the 1100iS for a cheaper price than the HRM-6’s and don’t mind their less-isolating nature, I’d say they’re a safe buy.
I’d also recommend considering the Beyerdynamic Custom One Pro, the DT770, and the Sennheiser Urbanites, if you’re after bass without sacrificing detail!
Good luck in your search!