Unfortunately, this does not appear to work with the X, either. From the User Guide as downloaded from the SanDisk iXpand site:
Works with
IPhone 5, iPhone 5c, iPhone 5s, iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPad Air™, iPad mini™, iPad mini 4, iPad Pro 12.9", iPad Pro 9.7" iPad with Retina display, iPod® 5th Generation and newer, with Lightning connector and iOS.
And under Device Compatibility on the site, the following is listed:
The following iPhones and iPads are compatible with the iXpand Flash Drive
iXpand and iXpand Sync application
iPhone 5, iPhone 6, iPhone 6 Plus, iPhone 7, iPhone 7 Plus, iPhone SE, iPad Air, iPad mini, iPad mini 4, iPad Pro 12.9 ", iPad Pro 9.7" iPad with Retina display, iPod® 5th generation and newer, with Lightning connector and iOS 7.1+
iXpand USB 3.0 and iXpand Drive application
iPhone 5, iPhone 6, iPhone 6 Plus, iPhone 7, iPhone 7 Plus, iPhone SE, iPad Air ™, iPad mini ™, iPad mini 4, iPad Pro 12,9 ", iPad Pro 9.7" iPad with Retina display, iPod® 5th generation and newer, with Lightning connector and iOS 8.2+
iXpand Mini and iXpand Drive application
iPhone 5, iPhone 6, iPhone 6 Plus, iPhone 7, iPhone 7 Plus, iPhone SE, iPad Air ™, iPad mini ™, iPad mini 4, iPad Pro 12,9 ", iPad Pro 9.7" iPad with Retina display, iPod® 5th generation and newer, with Lightning connector and iOS 8.2+
See,
https://kb.sandisk.com/app/answers/detail/a_id/17174/
So it appears the iPhone X is out of luck here.
Thank you for the suggestion, though.