IIRC, they are from the same question bank, but you select which test you take and the results are valid only for one, not both.

Most people who want a GI cert simply take the tests back-to-back, since the studying is the same.

GI certs are worthless unless you:
a) Are not getting a CFI cert soon (finances) and
b) Already have a job lined up teaching ground school

Not sure I'd spend the money on the test if you don't need the cert for a job.