Jordan Mills had a decent rookie year, had a foot injury last year and really fell apart. They felt it was the injury and he would be better this year if healthy but has not been. Have read several blog type posts on him and reviewed fan messages on several boards and they all say the same thing. Decent run blocker, awful pass protector. Definitely doesn't fit the mold of a true swing tackle...as someone else posted, he probably only sees the field as a right tackle.
I just watched all of his preseason snaps and his full game against the Bills last year which had him blocking Mario Williams.
Williams is one of the best 4-3 DEs in NFL and he only had 1 sack in that game.
His pass blocking in the preseason looked decent in terms of effectiveness. It is not always pretty and if the QB holds to that ball for an extended period of time he can have problems, but he'll get a good initial pass block and not let the pass rush have a free shot on the QB.
He is a strong run blocker but is sometimes too aggressive and will try to overwhelm the defender but end not getting a square hit on him which allows the defender to slide off the block.
There is obviously a big question about him being a swing OT because playing the left side might be a problem.
He could probably start at RT in game 1 and hold up OK.
They might have to have Free practice some at LT and move there if something happened to Tyron with Mills replacing Free at RT.