Leaded engine additives

I use one of these on my Tdi 300 but they also work with unleaded:http://www.doringindustries.com/main.htm

Thanks fellas, appreciated.
While on the subject what leads do you use on your landy ? Eagle, Topgun, etc ?

I had a old 1968 Valiant a few years ago and 98 premium petrol and performance leads made a world of difference to it.

Same for a landy ?