There are several good reasons to use One-Step

It is a fast, easy and safe method

An obturator, is defined as a plastic core surrounded by thermoplastic gutta percha. It is a fast, easy  and safe method to make a  perfectly sealed root canal filling.

Because the solid tapered plastic core ensures:
- that the gutta percha is carried all the way to apex
- that a certain lateral pressure, is pushing the gutta percha out into the side canals

Fast Heating an obturator takes 1 min.
You can place 4 obturators in the heater at the same time.
It only takes 10 to 15 seconds to insert an obturator in the canal.
Easy Lock the One-Step Tweezers at the predetermined working length on the shaft, so that the edge of the head of the Tweezers is placed at your reference point for your working length. The edge of the Tweezers' head is used as a traditional rubber stop.
Now you only need to insert it into the canal.
When the guttapercha is set after 4-5 minutes use the tweezer to break off the obturator in the chosen length. 
The rest of the cores stays in the canal.
Safe More than 5 mill. root canal fillings have been made with One-Step and 20 mill. root canal fillings with Soft-Core, and safety has not been an issue.
Allways take a control xray to be sure you have placed the obturator all the way to apex and made a perfect seal.