I bought the Gunson 'Workshop Timing Light' from halfords. Was pricey but its bullet proof and you just dial-in the advance you are after on the back of the gun. Very simple to use. I intend to service my van regularly for many years to come so I just tend to buy quality and buy once
Most marks on the lower pulley are set at 0deg, 5 deg & 7.5deg, the advance on the gun means you can set it to 5 deg advance and zero it to the 0 deg notch