I use Fibracells (all Premiere 1 1/2) on clarinet and alto. I recently came across a soprano set-up that plays pretty good, too. Clarinet - Lakey 5*; alto - Brihart Ebolin 3; soprano - Super Session E.
For me, the trick is to find the right mouthpiece for Fibracells. I have a ton of old mouthpieces for each instrument(s), so I could experiment easily enough. The pieces I found that work well with Fibracells don't work so good with cane (a personal opinion, but all mouthpiece choices are personal). If I went back to cane on clarinet and alto, I would be using different mouthpieces.
For instance, the pieces I use now with Fibracells are all fairly closed in tip-openings. The pieces I use with cane are much more open.
I can't say much about high or low pitch, if you mean tuning pitch. If you are referring to tone (like bright vs. dark), that is subjective to the max, meaning that everyone hears those tonal qualities differently. But when I find the right mouthpiece for Fibracells, they play on pitch, are very responsive, and offer superb volume control. The tone is equal to my cane set-ups.
As far as choosing strengths with Fibracells, that too is a personal matter. Much depends on one's own embouchure. I've always gotten the best and fullest sounds out of softer reeds and found the 1 1/2 strengths (SOFT for the older Fibracells) worked great for me - again once the right mouthpiece was found. My Fibracell mouthpiece choices are not limited to the ones I listed; suffice to say I have others that work nicely with Fibracells, but not all. DAVE