I’ll assume you mean the film "300" (Zack Snyder, 2006) and are looking for a reliable, legal way to watch it rather than pirated or unsafe sources. Below is a concise, actionable guide.
Gamifies the "300" concept. The app tracks how much data a user has saved by downloading the 300MB versions instead of standard 2GB HD rips.
Understanding Moviesflix 300 Exclusive: Features, Risks, and Legal Alternatives