Kerrstinn is one of my all-time favourite plugins. My reasons are as follows:
(a) Kerrstinn sounds beautifully rough, dynamic and musical. (b) It's a breeze to use. (c) The presets (aka generators) are fantastic. Pick Freaky 4 or Circle Teller if you're in doubt, but each one of the presets does something unique and exciting. (c) The author was incredibly helpful when I contacted him about Kerrstinn. (d) You really need to hear it to believe how original and musical it is. (e) There's a great youtube tutorial if you're in any doubt as to how it works.
Possible limitations: you need a sequencer/VSTi host that can send time info; the generators are hardcoded: you can't just generate your own (though Johan welcomes suggestions in pseudo-code).
Kerrstinn has been rock solid on my setup though I get an occasional (rare) feedback noise from Cubase before selecting a wave - never when a wave is loaded and you're ready to record.
How is it used? You begin by selecting a *.wav file. Then you state how many bars it contains and how many slices you'd like to see used (bars x 8 tends to yield good results, but other settings will work fine too). Next you can set a number for the random number generator, specify the intensity of processing that takes place (values in the 90s can be fairly extreme) and pick one of the preset generators. Finally press play on the sequencer and you're ready!
How does it stack up to the competition? It's simple: if you send all four bars of the Amen break to other loop glitchers, you get beautifully shaped drum & bass. With Kerrstinn, it's early jungle reflecting back from a metal ceiling in a claustrophobic London record shop.