I'm not a clencher specifically because I can't find comfort with or without the softy bits.
With a bare stem, it's too hard to be comfortable on my teeth for long. With the softy bits, I find they force my mouth open wider, and I can't form a good seal around the stem with my lips (or it's incredibly awkward to do so).
The only truly comfortably stem I've been able to clench is the cheap plastic stem found on some Missouri Meerschaum cobs. But of course, those aren't durable, and can cave inward rather quickly.