Suppose I am sight-reading this piece.
With the second version, there is zero chance I will get the tempo change correct as I sight read.
The first version prompts me (especially if I'm familiar with how metric modulation works) to start counting in quarter notes rather than half notes during the 6/4 measure, and then I now can continue in exactly the right tempo as I am already counting quarter notes in the new tempo. The truth is that I probably still won't get it right on the first or second read, but I'm terrible (and inexperienced) at this.
It probably doesn't matter for someone who is going to study the piece before playing it, but you might be surprised at how often (in my experience, almost always) musicians will sight read a piece before studying it.