SimilarWeb is the go-to tool for estimating a competitor's traffic volume and channel mix when you do not have access to their analytics. For adult-market research it is particularly practical: you can benchmark a new tube or affiliate landing page against established players, see which traffic sources they over-index on (organic, direct, referral), and model realistic traffic targets before committing budget. Traffic share data and engagement metrics help validate investment theses.

Estimates become less reliable for smaller sites (under ~50K monthly visits) and pricing for the Web Intelligence plan is enterprise-level. The free tier gives enough data for orientation work.