I have the W505 installed with the Blackbird II. Before I have used a Megallen 4250 and the Harmon Kardon GPS 810. Let me say this, the blackbird II does not compare to these 2 GPS. But I have to use the BlackBird because I don't extra stuff hanging on my windshield.
First thing, docking the blackbird to the W505 is very simple. Open the face plate and insert. But it is recommended to install the optional antenna to the back of W505. It is the only way to get a excellent reception. Without the antenna, the reception is horrible.
Docking the Blackbird with the W505 does give you the large screen size, but does not increase resolution. Therefore the map looked pixelated.
Calculation of route is fast and accurate. You get choices of fastest time, and less use of freeway. Blackbird does not annouce the street name or freeway. Re-routing is also fast.
Traffic is optional, free for 90 days. It does show you where the traffic is, but somehow it is not as accurate.
Docking the Blackbird also give you the capability of bluetooth handsfree. It connects to your cellphone thru bluetooth, and sync with your phone's phonebook automatically. You can connect the optional mic to the back of the W505 for complete handsfree operation, talk thru mic and hear thru car speaker. And when receiving call or calling someone, it gives you the option to send the call back to the phone for private conversation.
POI searching is not as intuitive, you have to type the exact wording of the place you are searching or it will not come up.
The blackbird does have some good tool. There is a information tool that tells you your speed, how long have you been driving and idling, fastest speed and average speed.
Overall, the blackbird is a good compilment to the W505 if you are like me that don't like extra thing hanging on the windshield. Good GPS overall, but it just does not have the cool features of the Garmin or Magellan.