Lest I confused anyone with too much choice (classic me)...the difference is, where the Sonic Bloom--and it's oscillating counterpart, the Sonic Shroom--stays in high gain territory, the Arc Flash very easily and quickly goes from cleanish to dirty to muffy to distortiony to splatty. It's a great little Swiss army knife of tones, and I'm doing about a dozen. A few are already gone.
Just two in the classic zodiac girl graphic (one is sold):

And a few in this new lovely graphic:

http://FuzzHugger.com/stock
http://FuzzHugger.com/pedal-arc-flash.html