I you have the experience to identify and evaluate a 5th wheel. Then buying used is OK. But if you lack the knowledge and don't know what to look for. Or even what you are looking at buy new.
THere are bargains to be found on the used market, there are also plenty of leaking money pits. If you If you have the knowledge you'll be fine.
If you lack the knowledge by new from a reputable dealer.
19'Duramax w/hips, 2022 Alliance Paradigm 390MP >BD3,r,22" Blackstone
r,RV760 w/BC20,Glow Steps, Enduraplas25,Pedego
BakFlip,RVLock,Prog.50A surge ,Hughes autoformer
Porta Bote 8.0 Nissan, Sailun S637