Shane Zylstra ended up on the Lions IR list last summer after he cleared waivers.
Because Zylstra was an ERFA, there's practically no downside to the Lions re-signing assuming that he was cleared medically by the Lions medical staff.
Because Zylstra has versatility on Offense and contributes on Special Teams, if he's at or very close to where he was prior to the knee injury he suffered in training camp, he's a viable contender for the Lions # 3 TE position or a backup versatile piece on Offense. It's good to see him back.