I decided to use Concern Garden Defense, a good quality neem product. I sprayed the plants every few days for 3 weeks. Unfortunately, the bugs weren't bothered at all by the neem and they continued to lay more eggs until the population rose to infestational levels.
1 month later - a damaged Purple Tomatillo plant
After spraying a few gallons of neem on this poor plant, picking off the cucumber beetles and hunting for their eggs underneath the leaves twice a day, I decided to try another product.