Simon is best known for his VPN investigations and other research into online censorship and privacy issues. Some of his most notable studies include:
- The Global Cost of Internet Shutdowns in 2019, which found that this form of censorship cost the world economy over $8BN last year.
- Global Mobile VPN Report 2019: a world-first study of mobile VPN download growth across 70+ countries with year-over-year data back to 2016.
- VPN Ownership Investigation, which found nearly 60% of the most popular free VPN apps had hidden Chinese ownership and its 2020 follow-up.
- Free VPN Risk Index (Android Apps): Simon tested 150 free VPN apps and found 25% suffered DNS and other leaks, while 85% were potentially unsafe.
- Collateral Damage in the War Against Online Harms: co-authored with Open Rights Group, this investigation into overblocking of websites by UK ISPs revealed over 400 charity, school and social supports sites had been blocked in error.