What is the difference between a piercing clip and an angled bed of nails cordset?

The most commonly used piece of test equipment in a lineman’s toolkit is the butt set. This handy little device is intentionally built by manufacturers to withstand some very nasty weather, since a lineman or cable tester is often outdoors performing line testing in the elements. The butt set also has some extremely useful functionality, including testing for continuity, over-sized belt clips to make them convenient to carry, memory storage and retrieval, indicators for polarity, a button for pausing, previous number redial, amplified speaker, and two-way speakerphone for hands-free communication.

Source: Blog.T3innovation.com