I've noticed some problems with Opera Mini 5 in particular: its inability to download from certain links and worse still its inability to use the Yahoo! search engine. It also cannot use the Youtube search engine.
Fact is, these two browsers still get a lot of use if other forums are any indication. For example, they can be used on Windows devices via Bluestacks and other emulators, and Opera Mini 8 is popular with users of Puppy Linux via Microemulator (JAR). Relatively little power and especially safety- and the ability to keep that stupid ad-script at bay (a BIG problem with Youtube nowadays!)- are reasons people like this browser in all of its forms.
These browsers absolutely give new life to old devices, which is great for those stuck with older devices for any reason. Can they be kept up to date?