Yes would buy ... but wouldn't pay a huge premium over economy. Same as my opinion for AirAsia.
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I have tried both the AirAsia Y and flatbeds, and would try them again if the price is right. The flatbeds are excellent and big improvement over Y from full service carriers.
I think they are selling quite well -- I'm travelling tomorrow (Y unfortunately) and the flat beds are sold out but still seats left in Y.
I was under the impression that Jetstar already offered them:
[video=youtube;bMTllQ9_rOw]http://www.youtube.com/watch?v=bMTllQ9_rOw[/video]
Apologies for the poor quality of video. Was the best I can find.