The new form factor is aimed at ultra-mobile devices like smartphones, IoT gateways and embedded systems. XFMEXPRESS NVMe cards will be slightly bigger than microSD cards, but the transfer speeds should match the M.2 form factor devices, with theoretical maximum bandwidth of 4 GBps (first gen) or even 8 GBps (second gen).
https://www.notebookcheck.net/Toshiba-intros-new-XFMEXPRESS-form-factor-for-PCIe-NVMe-SSDs.428823.0.html