Nowt wrong with watching the DVD, just be aware that other companies sell similar stuff. If it shows you how to set up the mechanics of the rig then it will have been useful.
As for safety, I have used inlines for many years, often in weedy situations and have never had a problem. Provided it has been set up correctly I find an inline set upto be one of the safer set ups.
I've seen plenty ofchod, helicopter and lead clip rigs which have made me shudder, paricularly when used with lead core.
There are lots of books and web sites which deal with the subject of safe rigs. This site has a section dedicated to rigs, as Roto says, make sure you take a look at it.