Mangini was New York Jets head coach from 2006-2008, a stretch in which Ellis didn't miss a game for the team, totaling 118 tackles and 18 sacks.
Before that, Mangini was defensive backs coach (2000-2004) and defensive coordinator (2005) in New England, so he knows the roots of Bill Belichick's system.
"I think it's a really good signing for New England because Shaun has more experience in this family than probably anyone else they could go get," said Mangini, who has joined ESPN this season as a football analyst.
"He was drafted by [Bill] Parcells, played for Al Groh and played for me; there is a lot of similar terminology and he has a ton of experience. It makes sense. The learning curve shouldn't be very big."
If the Patriots were running their standard 3-4 defense, Mangini sees Ellis as a good "run-stopping end," with his best fit at Ty Warren's old left end spot. But Ellis also has flexibility to play on the right side.
"He has versatility, he even played some outside linebacker for us when we wanted to get really big," Mangini said. "We'd stand him up over the tight end and he can kill guys. I don't know if that's something Bill [Belichick] will do, but he can do it and do it well. He can drop into coverage; he has that type of athleticism in the base [defense]."
When the Patriots are in a sub defense, which they were about 57 percent of the time in 2010, Ellis offers other options.
"He can play down, inside, outside, which adds another layer of versatility," Mangini said. "He's a good pass-rusher, a physical guy."
Another possibility is a more traditional 4-3 style defense, and Ellis has proven he fits there as well.
"He could play end in that system," Mangini said. "That's where he played in Rex's system [with the Jets]. Rex runs a 3-4 but with 4-3 spacing. That's what Baltimore does, what Pittsburgh does, it's 3-4 personnel but set up like a 4-3. That's another reason Shaun makes sense. He has a comfort level with that. He's a unique guy. You can do some creative stuff with him that you couldn't do with a lot of defensive ends."
Mike Reiss covers the Patriots for ESPNBoston.com.