I had the Z-1 installed in my 2006 Acura RSX Type-S about 6 months ago. It was a professional install at a local Car Toys, but the technician found that when he connected the speed pulse wire to the VSSOUT on my ECM that my speedo stopped working! I did some testing over the weekend (after taking it back 3 times with no progress!), and found that the Z-1 was not even getting a pulse when the speedo was knocked out. 
I've contacted others who have installed a Z-1 in the exact make/model/year vehicle and didn't have this trouble... makes me wonder if my Z-1 is defective? (I HOPE NOT! I don't think I can even drive without it anymore...)
Has anyone had this issue with the VSS connection? I heard something about splicing into the cruise control wire - but this sounds a little risky to me. 