Quick Tach Q......

I found a tach that looks like a pretty good deal. www.summitracing.com (part# SUM-G2905). For suggested parts, they say tach adapters, that are both around 70 dollars. Do I absolutely need one of these? I always see people just wiring it into the green wire by the coil. So do I really need to spend that much cash?
Thanks alot, oh also, what do you think of that tach/shiftlight?
 
The Tach should work fine. If you are using an MSD, or other aftermarket CD ignition, you will need the adapter for your stock Tach, and may need it for the Summit one as well.