Mono's greatest drawback is its garbage collection which wasn't sorted since its first version, this only is a reason not to use it on mobile devices.

I must command the bloke who wrote the article but he should have provided more details like how he performed the tests and benchmarks.

Last Dalvik was designed to work on low resources ARM devices, it can probably be ported to run on x86 systems, but it won't take their full advantage. Mono wasn't designed specifically for that purpose (running on a low resources device) which makes Dalvik a better solution. I'll give an example take a proper 4x4, an AWD SUV, and a Sedan. The 4x4 will go anywhere and will prove to be a great instrument in exploring the off road, on the highway it will suffer from low grip, terrible handling, a low gas mileage. An SUV can be taken off road, but isn't capable to pass hard terain, while on the highway it will go better then a 4x4. A sedan will do well on the highway but taking it down to the beach can result in a misfortune.