Vellocet, the German plastic training rounds are very loud and produce a very healthy muzzle blast/flash. Even though they're only 10gr slugs, they're supersonic several times over (some indicate around 4000 fps).
They do make for wonderfully inexpensive plinking ammunition. They will atomize a 12 can of disgusting Fresca at 20 yards and the POI is about the same as lead and copper fodder at that range. I understand they are accurate out to 100 yards. I haven't tested beyond 25 yards, but from what I'm getting now, I wouldn't doubt those claims.
The downside is they remain lethal for a good ways (though surely less than traditional ammunition) and are entirely too loud for back yard plinking if you have nearby neighbors. Also, for whatever reason, some rifles will exhibit issues ejecting the spent cases. They will feed, fire and extract just fine, but the extractor seems to drop the spent case before it contacts the ejector, so they tend to sit atop the rounds in the mag, requiring the user to tilt the rifle to spill it out the side.
Still, $7.99 for 50 rounds still seems like a good deal. I'm probably going to place another order of 1k though I still have more than 700 from the first 1k order. I don't think it's being made anymore and it's obviously destined to go the way of inexpensive 7.62x25 surplus ammunition: cheap and plentiful one day, expensive and scare the next.