Jackson strikes me as a boring, low upside option. Odds are he can give you 200 innings at a 4.50 ERA, and be a guy you won't want starting a playoff game if you make it that far.
How many playoff teams in the last 3-4 years have been able to get through a series while starting only pitchers you'd rather have than Jackson, I wonder? I bet it's a very short list.
Obviously value there, especially on a 1-2 year deal, but e strikes me as back end guy more than anything. There has to be a reason why he's been on every team in the league.
A good part of the reason is that he's been involved in deadline deals two out of the last three years, in both cases as the key piece for the "buying" team. He rewarded both transactions with solid performance down the stretch, and one of the two teams made the playoffs (and won the WS).