I'd definitely go for the bluebus over grom all day after buying the grom unit. I initially bought the grom unit because it had the feature to show what song is playing and wasn't keen on the cheap ebay unit. Unfortunately it bugged out my navigation screen and would prevent the use of the menu. My understanding is that not all radios are affected. In order to fix it you have install a little jumper on the circuit board but it removes the song title feature... Sometimes it bugs out and I have to reboot spotify in order to hear any music. Another annoying bug is that my prev/next song buttons don't always register. I have to press them multiple times on occasion which is annoying. The bluetooth sound is flawless though so no complaints there.
$150 Grom vs the $18 BT ebay module... definitely get the $18 module. Gets you the basic bluetooth audio and radio button integrations. For $200 more, the bluebus basically gets you more features, customizations, and overall much better refinement. It has bluetooth autoplay when you start the car which is actually something I wish the grom had.
This guy reviews the bluebus and compares it to the grom (which would also be valid against the cheap ebay module)