Opera Mini is one of the easiest and simplest browsers to use before high speed wireless connectivity became the norm. Many people actually loved that their GPRS and EDGE-enabled phones were able to surf the net.
You just type in the URL and the website gets compressed and displayed on your phone. Pretty cool during those times considering that phones were not as powerful as those that we have now.
Now that the Opera Mini will be featured along with Amazon Silk in Google Chrome, these browsers will definitely catch the interests of many developers as they are slowly becoming open source. Had Opera Mini done this a long time ago, who knows if it could have developed the way that Mozilla Firefox did?
Also, Opera Mini on EDGE will still be useful for people in countries that do not have high-speed wireless networks.