[Mr Gazza]

The one you linked to should fit a Monster, It looks like the one I have, but have not fitted.
Ducati did one as a kit that could be retro fitted, or you can adapt an ST2 one if you're a bit crafty.

The one in your link is missing a long bolt that goes in the normally empty, rearmost through hole in the engine cases. Sometimes there is a threaded insert in the right hand side of the hole, where a breather tube, wire guide is bolted.. The insert should just tap out with a long drift from the left.
You might also have to change the sidestand for a later one as the early one competes for the same mounting holes as the centre stand on the left side (the two M10 tapped holes.)

Don't expect a simple bolt on conversion, you might have to do some adaptions. It should just clear the exhaust pipes okay but the assistor arm might hit the left silencer.

I have a lower mudguard extension on my Sie and a floating rear brake torque rod, which make things very awkward indeed... I wish you better luck than I had.

Thinking more about the long bolt and through hole.. I believe that this picks up brackets on the exhaust on some later bikes, like 620ie.