according to Safecom`s site the drive is compatible with Mac and needs no drivers click here , however on their support issues list click here# they give formatting instructions.
The pdf manual click here states...
This USB Hard Disk is supported by the Mass Storage Support 1.3.5 in Mac OS.You do not need
to install any drivers for it.
If you are using Mac OS 8.6, the software of Mass Storage Support 1.3.5 is required to install.
You can download The USB Mass Storage Support 1.3.5 from the Apple Software Updates web
dont know anything about Mac`s so not sure if it is an issuse with file system, it maybe that Mac can only use the drive as read only if the drive has been formatted as NTFS, hopefully a Mac user can answer this for you.