Personally I think they're more hype. Dolby is pushing them because every one bought is money in dolby's pocket since manufacturers have to pay a fee to utilize the technology.
If you absolutely positively have no way to install speakers overhead they're better than nothing, but think of it like a surround sound bar, it definitely does sound significantly more expansive than plain stereo, and if you sit in the sweet spot you might just be fooled, but it's not true surround.
Most reviews of these have stated that the effect is more diffuse and ambient, actual overhead speakers sound much better.
If cutting holes in the ceiling is an issue, pick up a pair of Polk OWMs, you can either attach them to the ceiling using Hangman bar speaker screws, which can hold 30 lbs a piece in drywall, or attach them using the large Command picture hanging strips which cause no damage when removed. I have done it both ways, had the speakers hanging from those picture hangers for nearly 3 months and they never fell down, I've used them to hang much heavier speakers on the wall before without issue. Just use 3-4 strips, clean the ceiling well, and stick it up there.
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