I just got mine the other day from the previous FP deal and I have to admit that it's far from a must-have but if you already have a Bionic, it's a pretty slick device.
Build quality is superb and the unit is thinner and lighter than I expected. Screen quality is good but not spectacular--think on par with any Acer 11.6" Timeline or Aspire. Keyboard is a little small and shallow but the touchpad is quite good. Battery life is very good and the Bionic fits the dock quite well, even with the Moto extended battery installed. Performance is a bit laggy but surprisingly capable of playing 720p YouTube videos. Netflix plays from the Android app but it's not in HD and Netflix won't play in the full browser due to the lack of Silverlight.
Probably the handiest feature is that you can power the dock from your phone's internal battery as well as being able to talk on speakerphone while composing an email or text message from the fullsize keyboard. It's also nice to be able to utilize the blazing LTe connection to pull up fullsize web sites wherever you are without having to pay for a tethering plan or resort to hackery. I really really wish Moto had at least included some kind of trickle charge over microUSB capability so you could bring one AC adapter to power the Lapdock and the phone. Having to lug a separate power brick for the lapdock totally kills its portability factor.
I never would have paid the $300 or whatever these things were when new but for $80ish it's a no-brainer IF you intend on keeping your Bionic around for a while longer.