Pros:

• Completely free with no features locked behind subscriptions or paywalls
• Visualizes scholarly conversations
• Reveals a network between two similar articles

Cons:

• Requires an initial article to begin the search
• Does not directly link to full text
• Five sources are recommended for the most relevant results

Pros:

• Visualizes a scholarly conversation
• Identifies sources through a network of citations
• Connects articles with similar topics
• Suggests keywords for future searches

Cons:

• Useful filters (publication date and keywords) are locked behind a paid subscription
• Full text may not be available

Pros:

• No initial source required
• Simple language research questions as well as longer copy-pasted assignment prompts are supported
• Summarizes key findings from abstracts
• Filters available for publication date, PDF availability, type of study, and keywords in the abstract

Cons:

• Works on a "credit" system to conduct searches and more complex questions require more credits
• It is not possible to purchase or refresh credits on a free account
• Doesn't directly link to articles, and full text may not be available