I haven't used Hearty Bird yet, but I do like the company's products. I'm currently adding some Feather Fast for my straggling moulters.
My gouldians were/are also very finicky about different foods. Have you tried making your own egg food? This is only way I got them to take vegetables. It's quite literally just hard boiled eggs, smashed up with the shell included, and some type of drying agent to suck up the extra moisture. It took them a few days to get the nerve, but once they had a taste, they couldn't get enough. Once I knew they were comfortable w/the eggs, I half-mixed the vegetables into one side of the eggfood/plate and they finally started going for it. They seem to enjoy broccoli and cauliflower. I also give them carrots, spinach, kale, cucumber...haven't seen them really dig into these ones, but I can't be certain. To this day they still refuse fruits, so I can't help you there.
Speaking of Morning Bird products, have you tried their commercial dry eggfood? It's called Miracle Meal. This is what I bought when I was still waaay new to finches and panicked about "why they were losing all their feathers"...I didn't know what moulting was yet.

You'll know they're enjoying it when you see egg shell pieces and broccoli shrapnel thrown about the cage. I recommend lining the bottom with newpaper, paper towels, newsprint....something to catch the pieces that fly around so they don't stink up your cage when it's time to remove.
Hope this helps!