I have been making my own laundry soap for years. It works just fine. I rarely use Fels-naptha soap. I have been using Zote soap. It is similar to Fels-naptha. My mom uses ivory soap with no issues at all.
The only problem I have had was Fels-naptha didn't keep the whites really white. This was a combination of our hard water and the Fels-naptha. The Zote soap has been better for the whites. I also use about 1/4 cup of baking soda in the washing machine along with the soap when I wash whites. The baking soda helps soften the water and keep the whites whiter.
I also use the recipe for the small bucket but use twice the water and fill the big 5 gallon bucket and it still works fine.