Fantasy Upside
The thing about Matt Stafford is that he isn't going to win you a fantasy league in 2024. He's more "safe" than an upside guy in his later years as we get farther removed from the 5000-yard days in Detroit. That said, if you're in a Superflex league or in best ball, Stafford is far from the worst option later in drafts. He finished as QB15 last year without a healthy Cooper Kupp, so presumably outpacing his QB19 draft position shouldn't be impossible. Again, not a league winner, but a safe option in drafts.
Fantasy Downside
The downside is pretty simple, like Kupp, Stafford is getting up in age and has also at least considered retirement the last two offseasons. He's not your guy in redraft leagues as you should be able to do better than the QB19 in 1QB leagues. He only had three games with over 20 fantasy points last season, so while he's a safe option and has no threat of losing his job, he also isn't likely to win you a ton of weeks.
2024 Bottom Line
The bottom line on Stafford is that he's a safer option for Superflex leagues and a solid later-round stack in best ball if you've got Puka Nacua, Kupp, or both. He's an avoid in 1QB redraft leagues as you can certainly do better.