All normal Saniflo products rely on gravity in order to function. If you were to use one of these products in a low / level access installation then it would need to be sited below the level of the shower waste, which would be extremely impractical.
The Saniflo Showermatic pump actually sucks the waste water from the shower waste and therefore can be installed above the height of the waste itself meaning it is easily accessible and far easier to install. A guide to installation can be found here.
Noise is an issue that can affect level / low access suction pumps. However, the Showermatic utilises a patented peristaltic mechanism which means that it is virtually silent in operation.
No, the Showermatic utilises a patented "auto gully" that switches on the pump the moment water is sensed in the shower waste. The pump will remain on as long as water is there.
There are several ways in which this can be achieved. In most situations a low (40mm high) shower tray would require the addition of a riser kit (adjustable feet) to be fitted in order to raise the tray sufficiently for the waste trap to be fitted above floor level. In some cases you may find this acceptable, but the addition of these feet will raise the height of the tray to over 100mm, which may defeat the the whole purpose of having a low level tray!
As part of the Sanilife range of products Saniflo have developed a tray / pump combination that is only 46mm in height with nothing below tray level and yet can still evacuate waste water easily without either having to dig the floor or raise the tray. Details of the Traymatic can be found here.