The nice thing about Robert Henderson is that he is entering his prime. He turns 27 in November. The bad part is he has never played a regular season snap. Detroit signed him after he bounced around the league a bit, and for sheltering him on their practice squad a season, they have earned a seventh round pick. That is a good move. No doubt. The Lions are hurting at end, and so they didn't trade Henderson because of surplus, but, I presume, because they were happy to net a pick for a player that was indeed freely available.
Here is an excerpt from his Giants bio:
Played in 46 games with 33 starts at the "Bandit" defensive end position...Career totals include 173 tackles (115 solo), 13.5 sacks for minus 66 yards and 29.5 stops for losses of 123 yards...Forced 7 fumbles and recovered another...
He played at Southern Mississippi. His number are not anemic, per se, and the tackles for a loss supplement the sacks, but they also are not very significant for a player with middling tools. Southern Miss does not play a tough run of schools. You can see his production by opponent here.
What will become of this?
Henderson might be cut before the season starts. He should have remaining practice squad eligibility. He spent 2008 on IR, and has never played a regular season snap, and so should have one to two more seasons if Seattle wants to stash him away.
Henderson might become a rotational end.
The former seems more likely, but maybe Seattle is capturing Henderson at the right point in his career and by riding his prime, will get some value out of him. Without an exhaustive look, I assume there are ten Robert Henderson's freely available, but maybe not. Maybe Seattle saw something special in him.
The other matter is about the value given to get Henderson. I was just working on a post looking at how mid- and late-round picks are not likely valuable, but by hoarding them, a team increases the chance that any one might work out. According to this post from Pro Football Reference, an average seventh-round pick has about one-third the value of an early third-round pick. Not much.
Seattle did not spend much, and it does not look like they received much in return. Without knowing Henderson well, I can't be sure about the character of this trade, but my gut says that Seattle spent resources on a player they could have had for free.