Seems very strong to me. It gets Kerry on something that is inarguably part of the record–his Senate testimony. And the guys are talking about how the testimony affected them–also something that is inarguable. So I agree with the Democractic aide quoted in this Times story:

“Mr. Kerry’s campaign argued that he was relating accusations made by others and that he had since described some of his past remarks as excessive. But some Democrats said privately they feared that this ad would have even more impact than the last, whose charges have not been substantiated.

`It’s not something that can be easily or successfully discredited,’ said one party strategist, who requested anonymity because he did not want to be seen as undermining Mr. Kerry’s campaign. `It’s guys talking about how they felt and you can’t discredit someone’s description of his own feelings.’”