SimAudio NEO 400M Mono Amp?

I am just curious to see if anyone had listened to these amps?  I currently have the Moon W-3 and like it very much.I am looking to upgrade to another amp preferably also another SimAudio.  I like the idea of mono's since in term of practicality it's a lot easy to carry two 35lbs components than one big 70lbs. 
The 400M is advertised to have high efficiency but in high end audio it seems like if everything else being equal, the efficiency is almost inversely proportional to sound quality that is the higher the claimed efficiency, the most the sound will be adversely affected.  I also thought about purchasing the W8 but the weight of the amp is probably a deal breaker for me.