They seem to help extend the life of the tube as well. I fitted an e-starter in my kitchen light and the tube lasted for 20 years.
Unfortunately in that period T12 tubes had become obsolete and I couldn't find a replacement so the kitchen now has a new light with an electronic ballast and a T8 tube. (If you want to be bang up to date T5 tubes are also available.)
Well, I did find an online supplier who would sell me a pack of 12. As I only have the one full-sized fluorescent lamp I didn't think I'd get my money's worth.