1. Key Difference 1: Pricing Model: Amazon Mechanical Turk (MTurk) follows a pay-per-task pricing model, where requesters pay workers for completing individual tasks. In contrast, CrowdFlower (now known as Figure Eight) offers a subscription-based pricing model, allowing requesters to pay a set fee for a specific number of tasks or hours of work.

2. Key Difference 2: Worker Pool: MTurk has a larger and more diverse worker pool compared to CrowdFlower. MTurk attracts a wide range of workers, including those from low-income countries, while CrowdFlower focuses more on attracting experienced and skilled workers who can provide higher-quality outputs.

3. Key Difference 3: Task Complexity: CrowdFlower is better suited for complex tasks that require more cognitive skills and expertise. It provides tools and functionalities that enable requesters to create and manage complex workflows involving multiple sequential tasks. MTurk, on the other hand, is more suitable for simpler and repetitive tasks that do not require extensive expertise.

4. Key Difference 4: Quality Control: MTurk offers less built-in quality control mechanisms compared to CrowdFlower. While MTurk provides basic tools for filtering workers based on their approval rating and blocking low-quality workers, CrowdFlower offers more advanced tools like custom quality programs, test questions, and consensus judgments to ensure better output quality.

5. Key Difference 5: Speed of Completion: CrowdFlower generally offers faster turnaround times compared to MTurk. This is because CrowdFlower relies on a smaller pool of skilled workers who can complete tasks efficiently. In contrast, MTurk's larger worker pool may result in longer completion times due to availability and varying skill levels of the workers.

6. Key Difference 6: Task Distribution and Management: MTurk allows requesters to distribute tasks to multiple workers simultaneously, enabling faster completion. CrowdFlower, on the other hand, focuses on task management, providing tools to assign tasks to specific workers in a controlled manner, which can be beneficial for complex tasks that require specific expertise.

In Summary, Amazon Mechanical Turk and CrowdFlower (Figure Eight) differ in their pricing model, worker pool diversity, task complexity suitability, quality control mechanisms, speed of completion, and task distribution/management approaches.