I've done a fair bit of fermentation and IMO starter culture is unnecessary in most cases. I'd use it if I was fermenting meat, but for most vegetables it's unnecessary, especially given the cost. Once you've make your own ferment, you'll have juice from finished batches to add to the vegetables if you feel the need for starter culture.

I want to thank you for starting this topic. By following your links, I ended up changing my dental floss to Dr. Tungs. I am amazed at the difference in that floss. My mouth is so much happier!

ETA: From my research, inoculating a ferment with bacteria that ferments another type of product, like putting whey into a vegetable ferment, doesn't do much besides change the immediate level of acidity. Mercola's product has S. Thermophiles and L. Acidophilus both are milk fermenting bacteria with optimum temperatures far higher than the optimum temperature for vegetable ferments. I didn't parse the rest of the list, because the low hanging fruit was enough.