"متضعضع" - Translation from Arabic to English

Says that proof of its practical application is pretty shaky.
أشار إلى أنّ دليل تطبقيها العمليّ متضعضع جدّاً

A beat-up guitar like this speaks to the experience of its owner.
غيتار متضعضع كهذا ينمّ عن خبرة صاحبه