If you are using DAW or MIDI sequencer with Virtual midi support (like Cubasis or Genome) you'll like this app.
bs-16i is the Soundfonts player and Soundfonts are small sample libraries created specially for wavetable-based synthesizers.
The app itself doesn't give you any specials - it is just SF2 (soundfonts files) player with keyboard and some controls (filter,lfo, midi routing).
But when you combine this with Audiobus, Virtual midi and huge choice of free SF2 files in the Internet - it is gold.
The app itself has low CPU consumption so it plays nicely with Audiobus and other apps running.
Read this 13 pages thread on KVR forum to find links to cool SF2 files.
As long as SampleTank doesn't play well with background audio and with other apps like Cubasis, bs-16i is a great addition to expand your iPad sound library.