The iDM8 and iDM11 sound pretty similar, though the iDM11 arguably offers slightly better sound. Neither speaker is going to blow you away, but they're decent enough considering their small size and relatively affordable price tags (the iDM8 list for $60 while the iDM11 goes for $70).
In many ways the iDM8 is on par with, which costs a little more but has speakerphone capabilities like the iDM11.
Overall, I came away liking the iDM8 and think it's a pretty good little portable Bluetooth speaker for the money. However, as I said in my review of the iDM11, I'm a little more partial to that model and think it's worth spending the extra $10 on it.
That said, if you're smitten with the bulbous the design of the iDM8 and don't mind the missing speakerphone option, I have no problem recommending it.