RI- what bal tosif? The strings are allowed to be any color. There is a minhag and a chumra that the color of the strings should match the color of the beged, but you could technically have other colors and still be yotzei tzitzis without violating bal tosif. IMHO, it makes sense to say that safek deoraysa lechumra overrides that minhag.
Personally, I don’t wear techeiles, but for no other reason than most of our gedolim don’t. But from a logical and halachic perspective, all the arguments point to wearing techeiles.