I use a "jiont jigger" similar to the ones you posted and it has worked for the 6 frames I have built with it, I work with .035" 4130. People will tell you that it works poorly for butted bicycle tubing which is thinner. Mine has definitely deteriorated and I wish I had money and space for a mill to replace it, but it served its purpose, which was to get me building quickly and easily. I have had to make many modifications and jigs to get it to accomodate streamline tubing and offset notches and some other silly functions. But in hindsight doing that really worked to my advantage because I know so much more now about what I want and need for when I do get serious.
If you want to start building soon (which is the only way to learn imo) you have nothing to loose by getting one of those, Good Luck!