I think iDealshare VideoGo is the best app to compress MP4 to a smaller file size.
I like its batch compress function and compress with almost no loss of video quality.
It also helps to compress other video or audio formats like AVCHD, MOV, AVI, WMV, MPG, FLV, WebM, MOD, TOD, FLAC, M4A, WAV, APE, WMA etc