I've got one TN1 and one F18 on each side of the room. I tuned each of them individually, and have been listening to them individually. I gotta say, they sound an awful lot alike. I mean like almost the same. Or at least they can be tuned to sound the same. Given that, either my settings choices are poor or the extra $700 for the Rythmik is not worth it.
I attached photos of the settings that I'm using on the subs. With these settings, the two subs sound nearly identical to my ears.
HSU VTF-TN1 settings (one port open)
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Rythmik F18 settings
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