Just get Dice Player. It's free, plays anything, has pop-up player, supports subs and multiple audio tracks. As far as I'm concerned, it's perfect. What is this with the converting nonsense??? This isn't IOS or Windows Phone!!! Come on!!
The average Bluray runs about 36GB... Some of us "convert" to reduce the size to something manageable.
Also, many Blurays are authored with seamless branching. Resulting in many individual video files, all with randomly ordered tracks. As I am unaware of any android media player that can automatically parse the playlist folder in a BDMV file structure, you'd just get a bunch of random snipets of the movie mixed in with the hundreds of actor interviews and other extras if you tried to just play the Stream folder.
In another case, some people like to watch Amine (SP?) which, it is my understanding, the people that "upload" this stuff have taken to encoding it in 10 bit color with some rather impractical encoding settings (as much as 16 reference frames in some cases.) Last time I looked, your Discplayer doesn't support 10 but color (MX Player does though) and 16 ref frame encoding requires software decode and causes things to turn into a battery eating slideshow. So again, converting may be required to make the file manageable.
-Suntan