What's the main drawback of "concurrent think aloud," "retrospective think aloud," "concurrent probing", and "retrospective probing" approaches to usability testing?

1. Concurrent think aloud enables the moderator to develop a better understanding of which contents the participants are engaging with, what they are thinking, whether questions arise or what participants are feeling. So the major draw backs is to ask the user to speak continuously throughout the test.

2. Retrospective think aloud protocol is a technique used in usability, and eye tracking in particular, to gather qualitative information on the user intents and reasoning during a test. It's a form of think aloud protocol performed after the user testing session activities, instead of during them. So the major draw backs is to ask the user to retrace her/his actions after the test is complete.

3. Concurrent probing can be seen as a variation or more accurately an extension of contextual inquiry, the major draw backs is to ask the user follow-up questions whenever s/he says something interesting Ir does something unexpected.

4. Retrospective probing is a probing technique that can be employed to gain Customer / User feedback. It is a method, which follows Usability testing, Simulation, or other User testing methods to ask the participants their experience in hindsight. The manor draw backs is to ask the user questions about her/his thoughts and actions after the test is complete.