It's lighter than a single ring and guide.
It costs less than a standard single ring and guide.
Seems to keep the chain on as well as a guide so far.
Less places to clog with mud than a guide.
Easier to clean/remove/fit the chain than when you have a guide.
Fewer moving parts, less bits to break than a guide.
Chain and frame stay cleaner because there's no guide to gather gunk.
As ideas go, it's a very good one indeed.