We have some horses on Flaxseed and others that are not, it really comes down to what YOUR horse needs – each one is very different. Flaxseed is a great supplement but your post indicated that her coat and feet are doing fairly well. If the coat is just a little dull, consistent grooming without a lot of bathing will help. What a horse eats, if a good balanced diet, with bring out a natural shine along with little grooming. The feed might have some of the ingredients in it already but maybe not enough for a balanced diet. Read the ingredients and see what is in there and the amount in the feed. Remember to calculate the ingredient amounts with how much you are feeding your horse. Tribute feeds have several additional ingredients like probiotics, prebiotics and vitamins. I am not familiar with the Progressive Feed you are switching to, it would be worth a look to see what additional ingredients are added.
In you post you indicated that your horse had a long back, some colicy issues and suspected ulcers. That, in my opinion, is where you really need to look at adding a supplement. Flaxseed is great for coat and feet but really does not do too much for the GI track. There are hundreds of supplements to choose from, but you can start with the wizard or search products to cover what you want specifically. The long back may cause some stiffness in the joints and finding out if she has ulcers unless you have her scoped by a vet, it will be a trial watching her attitude and willingness as you try a product. The colicy issues can be helped with looking at what goes in her mouth (that is everything) and a supplement to help “coat or calm down” the system. If you call Smartpak and speak to someone that may help narrow things down for you too. There products are not just Smartpak products as you know. This is a very deep topic and hard to generalize but Yes, it sounds as though she would benefit from some kind of supplement.
Let me know if you have any other questions. Good Luck.