The felt pads on the recurve limb tips are to reduce the noise from string slap. I don't think they do much to reduce twang. You shouldn't have string slap on a longbow, because there shouldn't be any contact between the string and the limbs, except at the nocks.
I recently bought a Hoyt Satori recurve that came with limb tip pads. I didn't put them on at first, until I got tired of the noise. They didn’t help with the noise much, which was mainly twang. I replaced the stupid plastic bumblebee thingies on the string with real string silencers and it made a noticeable difference in the sound. Not quiet, but probably as quiet as I’m going to get it.
I haven't noticed much difference in noise shooting longbows and recurves 3 under vs split. Longbows are generally quieter than recurves, whether shot 3 under or split. 3 under is generally noisier than split, whatever the bow may be.