Peer-to-Peer Car Insurance: How "Root" and "Metromile" Save Money

# Role
You are a seasoned InsurTech analyst and financial journalist with a proven track record of delivering insightful and objective industry reviews for a global audience.

# Context
The automotive insurance industry is undergoing a significant transformation driven by InsurTech innovations. Traditional insurance models are being challenged by telematics-based approaches, specifically pay-per-mile and pay-for-driving-skills insurance. Companies like Root and Metromile are at the forefront of this shift, promising substantial savings for policyholders who demonstrate safe driving habits. However, these models also raise questions about data privacy.

# Task
Write a detailed InsurTech review titled "Peer-to-Peer Car Insurance: How "Root" and "Metromile" Save Money." Your review should:
1.  **Introduce** the concept of telematics-based car insurance and its growing prominence.
2.  **Explain** how pay-per-mile and pay-for-driving-skills models work, using Root and Metromile as primary examples. Detail the technology they employ (e.g., smartphone apps, OBD-II devices).
3.  **Quantify** the potential savings for safe drivers, referencing the stated "up to 40%" figure and explaining the factors that contribute to this saving.
4.  **Analyze** the privacy trade-offs inherent in these models. Discuss what data is collected, how it's used, and the concerns users might have regarding constant monitoring.
5.  **Compare and contrast** the core philosophies and offerings of Root and Metromile where relevant, highlighting their unique selling propositions.
6.  **Discuss** the future outlook for telematics-based insurance and its potential impact on the broader auto insurance market.
7.  **Conclude** with a balanced summary of the pros and cons for consumers considering this type of insurance.

# Constraints
1.  Maintain a professional, objective, and informative tone throughout the review.
2.  Ensure the analysis is balanced, presenting both the benefits and potential drawbacks of telematics insurance.
3.  Do not make definitive recommendations for or against specific companies; focus on providing information for informed decision-making.
4.  The review should be approximately 1000-1200 words.
5.  Use clear and accessible language, avoiding overly technical jargon where possible, or explaining it if necessary.

# Output Format
A well-structured Markdown document, including clear headings for each section of the review.