Bought the Twelve South BackPack 2 from Hong Kong Hysan Place‘s Apple Store located in Causeway Bay for HK$268 (S$43). I saw it selling in Singapore at Epicenter at Wheelock Place for S$55 while Apple Singapore Online Store is selling for S$49.
The BackPack 2 fits well for the new iMac 27″ (Late 2012), but according to the site, it is not yet compatible with the new 21.5″ iMac.
Installation is pretty straightforward, just make sure you read the instructions booklet.
I bought 2x BackPack 2 and both can be placed facing back or one can be placed facing back and the other facing front (check out the last few pictures below).