Its all about picking the right variety for your location. the save variety will not do well in the NE, Michigan, Cali, Texas and Florida. The growing times and climates are just far too different.
Between a friend and myself, we grew about 30 different GMO free heirloom tomatoes over the last two years. Some produced extremely well, some did very poor with everything in between. Some same varieties even fared differently from year to year due to the climatic conditions....here in SFla, having to grow in winter time can cause some bumps in the roads.
Oscar - I have grown both the green zebra and its "cherry" version. Its cherry version did phenomenal this year. Also grew black cherry, was a heavy quality producer last year but much less this year and was out produced by the aforementioned green cherry.
Bottom line, at least for us here in SFla, you need to selectively pick the heirlooms that will thrive here and then hope you have optimal weather conditions.