Crazy Memory usage on Transcend 128GB JetDrive 130 Expansion Card for MBA
As mentioned in my original question, the SD Association (of which Transcend are a member) cite performance impacts as a reason against using standard drive formatters. 

However, they have a formatter available for download at https://www.sdcard.org/downloads/formatter_4. On Mavericks, I reformatted my drive using this utility and recopied my files.

The results were as follows:


A single file 14.57GB took 4 minutes to copy. This is the exactly as advertised 60MB/s write speed.
80k files (16GB), however took 92 minutes to copy. which reflects about 5MB/s


In both cases, however, the info window was as expected showing a reasonable amount of memory usage and memory remaining. So, this solved my original problem.

As a comparison, I decided to reformat as a Journaled and found the following:


14.57GB file took 10 minutes to copy, which is only about 50% of the advertised max speed.
80k files (16GB) more importantly took only 10.5 minutes.


For me, sticking with a Journaled format is a no brainer, particularly if writing lots of small files, which I will be. It also may allow me include this on a Fusion drive, although I haven't investigated this yet.

TL;DR - It is probably best to reformat to a Journaled partition as it provides a more consistent write speed of about 30MB/s, no matter the file sizes. ExFAT ranged between 5 to 60 MB/s speeds, depending on the number of files being written (lower number is faster).

UPDATE: Transcend replied to recommended a replacement.