I"m the same as a couple of posts already on this thread. I feed the Fromm 4* range and have been so pleased with it. We had problems finding a supplier for a long time, and so I did a lot of research on cost etc and found that petflow was definitely the cheapest way of doing it for us. I am VERY impressed with their delivery time and I like that I can schedule my deliveries for a regualr number of weeks. We always make sure the next delivery is here well before the current bag is finished. If you think you will run out before you expected, you can go online and immediately change your delivery date to a day that is sooner. Another reason why I like the Fromm 4* is that it is for all life stages - so when we got Daddy from rescue we started to change him over to the Salmon Fromm that Maggie was on over a two week period and he is doing very well on it!!
Sorry I can't be of any more help on Merrick as I don't think I've ever seen it mentioned on this site before.