Disclaimer: As with all audio experiences, this is purely subjective, and dependent upon individual equipment, room, HRTF, and, most importantly, bias/prejudices. Also, I do not receive any monetary compensation for the advertisement or sale of consumer electronics.
I find any "atmos-ready" (i.e. simulated by reflection) systems, whether they be X.1.2 or X.1.4, to be ineffective and a waste of money at best, or gimmicky and distracting at worst. Even the best designs suffer from a multitude of acoustical problems, and require very specific room construction to be even somewhat effective. Your money is much better spent on professional calibrations (if you do not have the necessary equipment and understanding of acoustics to do so yourself), multiple subwoofers, better subwoofers, and proper acoustic treatments. If you want to get a good idea how these atmos-ready speakers sounds, get small bookshelf speakers and prop them up at angle on your mains (try to aim for the point on the ceiling that will "bounce" directly to your seat, a-la billiards). I actually found this to be a better solution than dedicated off-the-shelf solutions, because you can adjust the rake for proper angle given the geometry of the subtended angle formed by you front speakers and your listening position. If you're itching to add channels, I think adding "wide" DSP-derived channels would better serve 90% of rooms more so than any amount of reflected-based "height" channels.
Regarding "real" atmos (in/on-ceiling).....it depends on the room and equipment. I use on-ceiling speakers in my dedicated theater and living room, and tried every combination possible, and found X.1.4 as the only option worth the cost/effort. X.1.2 by comparison didn't offer much that wasn't already accomplished by previous DSP's: Dolby PLIIz, Yamaha Presence, or Audyssey DSX. It wasn't bad......but it didn't add enough to the experience to warrant the $100's/$1,000's required for the upgrade. However, in my experience, for smaller rooms (less than ~11'x11') where seats are against/near the back wall and large atmos-speaker/listening angles yield very short distances from each other on the ceiling, a 5.1.2 system MIGHT work.....but I think in that case switching to high-mounted dipoles sides in a 5.1 system would give much the same effect.
TL;DR: Avoid reflected-speaker solutions, sticking to traditional base channels instead (5./6.1/7.1). If you want atmos, stick to in/on-ceiling speakers, and only settle for X.1.4 unless you have a very small room and just feel the need to see the atmos/DS-upmix logos light up.
