Homemade curry roux won’t taste exactly the same as store bought brands, but it will come fairly close. Things that can affect the flavour include how long you cook the flour and butter for (longer generally means richer nuttier flavour), the brand of curry powder you use (the ratio of its spices) and the flavour of your other ingredients. Homemade also doesn't include MSG, so you may have to up the garlic salt, add a soy sauce or extra stock in the curry to get it close to how you like it.