The Mandarin Phonetic Symbols 2 (usually labeled MPS 2, MPS2, or MPS II) are somewhat confusingly named. MPS 2 is a romanization system. On the other hand, MPS 1, which is the original Mandarin Phonetic Symbols, is another name for the completely different zhuyin fuhao, which does not use the roman alphabet at all.
MPS2 has been abandoned, officially supplanted by Tongyong Pinyin. Curiously, advocates of Tongyong Pinyin often argued for their system by saying that Taiwan should use a romanization method made in Taiwan, not China. MPS2, however, was made in Taiwan.
MPS2 supplanted Gwoyeu Romatzyh as Taiwan's official romanization system in January 1986. (For more on this history, read the ROC Ministry of Education's booklet on MPS2.) Although it could be said that MPS2 was more widely used than its predecessor, this is only true because Gwoyeu Romatzyh was basically never used at all. MPS2 came to be seen on some highway and street signs but not really elsewhere. Taiwan's main romanization system during the MPS2 period continued to be a much weakened and largely useless form of Wade-Giles.
To the best of my knowledge, MPS2 has never been used outside of Taiwan.