Depends on location of the bushes some places can get away with solid with no real issues some you will have issues which can include breakages in extreme use.
Overall poly can be used pretty much anywhere without problem, it is a self lubing material, and will outlast rubber many many times over.
It will when used on suspension give a much taughter feel with less/no slop in joints so improves handling grip markedly for such a small outlay.
tabetha