Standard Java apps often suffer from jagged, blocky fonts. The "Extra Quality" mod injects custom font rendering engine rules to make text highly readable on 2.2-inch and 2.4-inch screens.
Standard Opera Mini versions frequently suffered from "Out of Memory" (OOM) errors on low-RAM devices. A "fixed" version contained modified internal memory management to prevent crashes during heavy browsing.
If you tell me the exact model of your phone (e.g., Nokia 6300, Samsung C3050), I can help you find the right installation instructions or even suggest the best version specifically for your device.