Is there a media player for android that can play an mp3 10% faster or slower if the user wants to?
Rockbox has a very early port to Android that allows speeding up an MP3 once the Timestrech option is enabled. The port is very functional, but the UI and integration with Android still leave much to be desired. Jon Corbet of LWN did a good summary article a few weeks ago. The most important piece of advice before using it:
Imagine that your screen is a 3x3 grid, where the middle is used as the selector, left-right-up-down are used as cursor keys. The other directions have special functions in some screens, e.g. in Now Playing screen with the upper left you can access some playback mode settings.
Having previously enjoyed Rockbox on a several previous Sansa players, I personally excuse the UI shortcomings and use it when playing long stretches of podcasts. I like that set the playback speed (independant of the pitch) from 50% of the original speed to (at least) 200%. In increments of a tenth of a percent. Depending on the subject and the speed with which people speak, I will listen to a podcasts at 175%, 166%, 150%, 133%, or 125%.
I wrote Osplay, which does this as its main feature. I consider it a stable product and am now only issuing bugfixes.
VLC For Android has a feature to play faster or slower https://play.google.com/store/apps/details?id=org.videolan.vlc&hl=en