Can you be sued for liable?

If I developed an “accessory” item that I claimed would make using a highly established product “more comfortable” ( both subjective terms), would this established product’s manufacturer have grounds to sue me for liable saying it could be inferred that I was downplaying the comfort (which is of no functional importance) of using their existing product?

No, you cannot be sued for libel (not liable). I assume you are in the United States. Comfort is an opinion and opinions are protected free speech.

Lots of businesses make products to improve other products. Think of all the manufacturers making iPhone accessories. Or padded seat cushions for automobiles to make Ford Focus seats more comfortable or making accessories to make automobiles look nicer and more “cool”. Have you ever heard of any of them being sued? No, and neither have I.

Dryer sheets make clothes dryers work better. Oil in a pan makes the pan perform better. Soft water makes soap work better. Get the drift?