I have been a witness of the true Yahweh of the Bible, but never been in the WT or associated with Jehovah of the WT, a false god concept. My experience is evangelical Christian from 18-51 years old.
A JW who becomes Catholic (there are similar parallels in these organizations) may be exchanging one religion/ritual for another. The person would be closer to the truth on virgin conception, Deity and physical resurrection of Christ, trinity, etc. They would have unbiblical ideas relating to salvation, Mary, Mass, purgatory, popery, etc. I am not Catholic because it is not the most biblical expression of biblical Christianity.
I believe there are Catholics that know and love the true Jesus and are saved despite Catholicism, not because of it. If one trusts Christ alone by grace through faith in the Catholic church, they can be saved (we are saved by grace/faith, not theological perfection). If one trusts the Mother Catholic church, priests, saints, Mary, good works, rituals, Mass, rosary, indulgences, etc., then they are trusting works, religion, self, not Christ. God will judge. Catholics are not in the same cult boat as JWs and Mormons because of their sound doctrine of God/Christology. The problem is that they add extra/contrabiblical traditions to Sola Scriptura (Scripture alone as authority). I would hope Catholics would read and pray and join a more biblical, pure church, but that does not mean it is impossible for a Catholic to be saved (essential vs peripheral issues). Many Catholics are biblically illiterate, hypocrites, nominal, and do not have a personal relationship with Christ, while others do, despite the other errors.
I agree with WT when it attacks certain aspects of Catholicism, but not on the issues that Catholics are right on (trinity, Deity/death of Christ, resurrection of Christ, Bible as the Word of God, etc.).