Usability testing is geared towards understanding how end-users interact with the software and ensuring a positive user experience. The primary considerations involve the system's ease of use, its consistency in design and functionality, and adherence to user interface design guidelines. UAT, on the other hand, determines if the system meets user needs, while load and compatibility have different focuses.

The "Defect Age" metric is a measure of the time between when a defect is introduced into the system and when it's discovered and resolved. It provides insight into how quickly a team identifies and addresses defects. MTBF (Mean Time Between Failures) measures the expected time between two successive failures of a system.

The "Record and Playback" technique involves recording user actions as they interact with the application. The recorded actions then form a script, which can be played back later. This technique is helpful for novice testers as it requires minimal scripting knowledge but is not always scalable.

Regression testing ensures that previously developed and tested software still works after a change. Given the repeated nature of regression testing, Automated Regression Testing is a suitable approach as it can efficiently handle repetitive test cases.

The primary purpose of developing test scripts in automation testing is to enable the execution of tests repeatedly without manual intervention. This ensures consistent test execution, efficient regression testing, and helps in validating application functionality across different test cycles.

Heuristic evaluation and standard user interface testing differ mainly in their method of analysis. A heuristic evaluation is a usability inspection method where evaluators, usually usability experts, compare a software product against a set of usability principles or heuristics. In contrast, standard UI testing is often scenario-based.

Automated testing significantly reduces the chances of human errors that can be introduced during manual testing. While it doesn't guarantee defect-free software, it provides a consistent and repeatable set of tests, ensuring that previously tested functionality remains intact.

Exploratory test cases are based on real-time learning and testers' expertise. Automation is not suitable because these tests are often non-repetitive, less predictable, and leverage the human ability to spot unexpected issues in an ad-hoc manner.

Test levels, which include stages like unit, integration, system, and acceptance testing, play a critical role in the Test Planning phase. They help in organizing the sequence and scope of testing activities, ensuring that all components of the software are thoroughly evaluated at the appropriate stages.

Automated testing involves the initial cost of writing and maintaining scripts, making it not cost-effective for one-time testing scenarios. While automation can handle large-scale projects and performance testing, it's not recommended when the requirements change often.

Security testing primarily aims to identify vulnerabilities, weaknesses, and potential threats in a software application. It is crucial for protecting data from unauthorized access and breaches, ensuring the confidentiality, integrity, and availability of the system.

Conversion Testing is focused on optimizing user actions to achieve specific goals, like making a purchase or signing up. In the context of an e-commerce site, a drop in sales and registrations post-redesign indicates a possible issue in the user's journey or experience, which Conversion Testing can help identify and rectify.