It’s good that it will have two parts of the mission, the impacter and the observer, but the article doesn’t mention if the measuring probe will get there first and determine any specifics of where to impact based on those readings, or if it’s just seeing the impact and afterwards and scientists will work backwards. Part of an actual deflection mission would be to know the rock you’re moving well inside and out way before doing anything. If this is a rubble pile type asteroid it will give a lot different results (and be harder to “stop”) than something more solid and/or metallic.

Also, “blowing it up” is much harder than it sounds, and if too late it could be in some ways worse than leaving it a single body to impact Earth, as enough large objects all reentering at once could be a major heating event in that area, potentially affecting more over a wider part. The movie version where the two halves split and narrowing miss the planet is total fiction.