Great starting point
If you were planning on reading Invincible and didn't have time to start from the beginning, this is the perfect jumping on point for understanding the plot--it recaps the first 21 issues. The only problem a reader might have if they start reading from this point is truly understanding the characters; in this issue most of the characters are just mentioned and understood from Mark's point of view.
However, it does allow you to understand the relationship between Amber and Mark better.