Traditionally LabVIEW has treated Strings and Unsigned Byte Arrays as being the same. This is nowadays a little unfortunate as all UI systems use some kind of encoding so Strings are not generally interchangeable with Byte Arrays anymore.
In trying to stay for binary data as much as possible with Byte Arrays instead of Strings, since that would be the sensible thing to do, the Unflatten from String (which should rather be called Unflatten from Stream) puts a totally unnecessary wrench into this.
I always had hoped that LabVIEW would change the default binary data stream format to a Byte Array at some point but this while it would be possible, is a fairly pervasive change that would require many backwards compatibility decisions that I unfortunately don't see NI going to spend time on anymore. This change however would be a very small change that has zero backwards compatibility concerns and almost no work to add to the existing LabVIEW software.
This same change has been for instance made to the TCP Write node some versions back already and could be also applied to the VISA Write!