My understanding of Sustanon is that it is testosterone bound to three different esters within the same compound. What's the benefit of that, and has anyone ever done a similar thing with 1-test?

The different esthers all have different half-lives, or release times, so a single injection will put test into the blood in a distrubuted pattern over time. This should give a steadier plasma level of the drug than a single esther.
1-T probalby won't be around long enough for anybody to bother putting it into anything besides the currently available prop and cyp esthers- which Sledge has combined.