  Three fibre feed integral field units (IFUs), called Slit Mask IFUs (SMI),
are being developed in the SAAO fibre-lab for the Robert Stobie Spectrograph
(RSS). The smaller, 200 micron fibre IFU (SMI-200) has 309 x 0.9 arcsec
diameter spatial elements covering an elongated hexagonal footprint of 18
$\times$ 23 arcsec is now being commissioned. The larger, 300 (400) micron
fibre IFU, SMI-300 (SMI-400), has 221 $\times$ 1.35 arcsec (178 $\times$ 1.8
arcsec) diameter spatial elements covering an on-sky area of 18 $\times$ 29 sq.
arcsec (21 $\times$ 44 sq. arcsec). In all SMI units there are two groups of 13
fibres offset by roughly 50 arcsec on either side of the primary array to
sample sky. SMI-200 provides a median spectral resolution of 2400 at
H$\upalpha$ wavelengths in a low resolution mode simultaneously covering 370 to
740 nm. At a higher grating angles the SMI-200 delivers spectral resolution up
to 10,000. A future red spectrograph arm for RSS will extend the simultaneous
wavelength coverage up to 900 nm at a median resolution of 6000 for the same
IFU. With this upcoming red arm and with the fibre-fed, near-infrared
spectrograph NIRWALS on SALT, SMI-300 enables wavelength coverage from blue to
NIR wavelengths at the same spatial resolution and footprint. The SMI units are
inserted in the same fashion as the existing long-slit cassettes at the SALT
focal plane. Prismatic fold mirrors direct the focal plane into the fibre IFU
and then back into the RSS collimator after the fibres are routed 180 deg
within the cassette and formatted into a pseudo-slit. Fold-prisms ensure that
the spectrograph collimator continues to see the same focal plane. In this
paper we report the laboratory characterization and on-sky
commissioning-performance of the first Slit Mask IFU, SMI-200.
