Yes, we are using writable volumes for a few years now. To be honest, one of theings we don't store is the OST file because users have a 10GB mailbox, we would end up with mail being stored in very expensive SSD disks, not really feasible .
Make sure to create the following registry key
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\svdriver\Parameters\DriveLetterSettings=6 (DWORD). This hides the drive letter for the writable but does give it a drive letter name. The driveletter part is mostly done for applications that don't install on a network drive (looking at you google). You could use other values and just disable driveletters for appstacks and writables altogether.
I would also suggest creating this key This shows the free disk space on the writable (and the amount a user can still safe on his writable) instead of the GI.
Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\svdriver\Parameters\ReportSystemFreeSpace=0 (DWORD).