Apologies to hear you guys are now stuck with Brandon Manning.
A quick breakdown: Most adequate 6/7 defensemen are usually "death by 1,000 cuts" sort of players. The Flyers seemingly have no problem with them in MacDonald and Hagg. Most of the time, these players won't do anything glaringly bad, but their small mistakes just add up over time.
This does not describe Manning. Every once in a while, whether it's a period or even a game, Manning will flash offensively and physically and you'll wonder why he can't stick as a 6 on a decent time. Then he'll do something just MIND-NUMBINGLY IDIOTIC and go back to being who he is. He will attempt to make plays that he just can't make on a regular basis, and it leads to noticeable mistakes.
Positives: He is physical and is always willing to stand up for his teammates. Not a good fighter, but always willing. He is legitimately a good character guy. Notice none of these positives are about his actual hockey skill.
Manning was an undrafted free agent who moved his way up the ranks from bottom pairing AHL defenseman, to AHL all-star, to 7th NHL defenseman. This should have been a feel good story for someone who started from the bottom and made his way to the NHL as a depth player. Unfortunately, he was overused by his NHL coaches, and public opinion on him changed.