I bought my Ethos in October 2012. I'm very satisfied with the sound. I think the Ethos is the ML speaker with the best price-performance-ratio, because it has an active woofer unlike the Theos, which makes a cleaner bass. The sound quality is excellent and the leap to the Montis is much smaller than the leap from a passive to an active woofer.
Both speakers are great.
I compared many active loudspeakers (Adam, Genelec, Neumann, KSDigital...) with the Ethos and the ML won clearly. I compared the Ethos with the Magnepan MG 1.7 and found the soundquality of both speakers great. The bass of the Maggie is a bit better integrated, but the overall performance of the Ethos is better, I think.
I would buy the Ethos again and I think that the smaller design of the Ethos fits my small room better than the larger Montis. But this is a very subjective view. You can't go wrong with both.