That was my first thought too - more of the energy available on the target rather than heating up the atmosphere and easier to target?
Then I thought, who fancies having a deathray like that up in space?
My other unrelated thought started out as - "When do they jettison their sails?", because when they get nearer the target, the solar wind from that star will otherwise slow them down & push them away?
It then moved on to "Sounds a bit like we are talking about throwing a message in a bottle over the side of a ship and expecting the bottle to end up on a particular beach the other side of the world".
Is that even going to be possible to predict all the eddies and flows of energy that will act on such a small payload over that distance to the target star system?
If "the ship" (our world) is in the wrong place when we chuck the bottle over the side (push the postage stamp craft with a laser), there may be no way to get it to land in the right "current" that will take it to the target destination anyway?