Yes, there are terrible metal and hard rubber clarinets out there: There are also hideous wood instruments, as anyone who has played a post WWII East German/ Soviet made horn with pot-metal keys can attest! However, the mitigating factors always seems to be quality of construction and attention to set-up rather than the material - I offer Tom Ridenour's pro line of Hard Rubber instruments, and vintage metal instruments by Noblet, H. Bettoney or Penzel Mueller as evidence. Tom's instruments have received a lot of kudos for pro quality detailing (like tone-hole undercutting) and, having discarded increasingly expensive and hard to find grenadilla, they are available for less than half the cost of the fabled R-13.
I suspect the factors that initiated the sub-par reputation of a lot of better metal/hard rubber clarinets were: poor mouthpieces and shoddy pad work. If the mouthpieces that have come stock with a number of my acquisitions are anything to go by, Martin Frost at his best would be hard-pressed to draw good music from their narrow tips and uneven facing! Original pad-work shows signs of being equally hurried, in some cases, with cheap pads poorly seated and opening heights at the mercy of whatever cork was on sale that week. Now, take that same horn, overhaul it conscientiously with leather pads and attention to setup and play it with a decent mouthpiece and I suspect you will be pleasantly surprised!
To be continued!