Whilst the FC5 and FC5 OPT are similar, the addition of the optical drive and its location in the case means there is some interference with the ZF240, specifically the ATX power cables as they exit towards the drive bay. Whilst it is possible to overcome this interference with some careful cable routing and adjustments to the position of the PSU, it is not a straightforward installation and should only be undertaken if you are comfortable with DIY. It may also require a short or angled SATA connector for the optical drive, for example – External Link
To reiterate, that there is no such issue with the standard FC5 and installation of the ZF240 does not have the issue detailed above.