There are those people who absolutely hate live blackworms. They see blackworms as a harbinger of disease and destruction, and will not touch them with a ten-foot pole. Some won't even allow fish that have been previously fed on them into their tanks.
Then there are those who swear by live blackworms. They use them on everything from breeding pairs to finicky new arrivals. Their young fish are raised on them, and they see live blackworms as one of the ultimate conditioning tools.
I personally fall into the latter of these two categories. Every single fish that I own has been fed blackworms at some point in its life. In fact I breathe a little sigh of relief when my fry are big enough to be fed blackworms and I can stop wasting time with things like baby brine shrimp and live food cultures.
A lot of people think live blackworms are a 'dirty' food and that by feeding them, there is a risk of introducing disease into their tanks. I think as long as you purchase your blackworms from somewhere reputable and store them correctly, the risk of disease is fairly low.
If you are concerned about the quality of blackworms at your LFS, ask to see them before you purchase. Healthy worms should clump together and shouldn't have an overpowering smell. If there are a lot of dead worms or the worms have a very unpleasant smell, I would advise you to look somewhere else.
If you want to cut the middleman out altogether, I have found the wholesalers that produce blackworms, will often sell direct to the public. This way you can get your worms straight from the source and not have to be concerned about improper handling or storage.
I have to say, in the two or so years of using them, I have never run into any issues. In fact, the fish that are fed almost exclusively on live blackworms are some of the healthiest and most prolific in my fish room.
So if you have been considering incorporating live blackworms into the diets of your fish, I say give it a go. You may be pleasantly surprised.
Hailing from Melbourne, Australia, I currently keep and breed a number of species from the coccina complex.