If you break yours (or your mate breaks it when borrowing your bike...) I can confirm that a reasonably cheap replacement, off ebay, fits just fine! Deckas, but likely sold under alternative names.
£14 posted. Decent price, decent quality, but I would use the original spacers and torque bolts:
VXM/DECKAS ISCG05 Chain Guide Top guide 30t-40t MTB, with additional hardware! | eBay
VXM / DECKAS ISCG05 Chainguide Top guide 30t-40t Mountain bike T6 6061 CNC Alloy. Weight: ISCG05 Approx 30g (Ex. Chainring Compatibility: 30t to 40t (round) 30t to 38t (Oval). It is fully adjustable to support round chainrings ranging from 30t all the way though to a 40t ring. ).
www.ebay.co.uk
£14 posted. Decent price, decent quality, but I would use the original spacers and torque bolts: