I got the one from SmartieParts too. They need a re-write of the manual. (The MDC one is in German, and the US one is for the 450.) Install takes about 30 mins if you know the tricks to it (below). If you can change a stereo, you can install this mod.
The key difference from the 450 are:
The speedo "pulls" out, just give it a yank, no screws on the 451.
The plastic housing bottom for the steering column pops off, the top has 2 T10 screws to undo from the underside.
You have to swap the white plastic "holder" on the cable harnes that goes into the speedo with the one already in your cars speedo (quick release the black pin part and its slides off.)
I'll have a full guide up soon (took pictures/notes during the install).
Just be sure your car is in park and has been off 5 mins before pulling the battery cables before install, or you'll get a mess when you re-power! :P