Upgrades
How can I put this without seeming cynical. $$$ thats why! Really though, this is a good solution to carry all the docs you might need around with you when not at the acft, and some you might not unless you can't sleep!
Current Cert D brought the avionics up to the spec that Gulfstream promised on day one. Cert E will be the first 'pay' upgrade but will give planeview an amazing 3d virtual imap amongst many other promised toys.