I bought some Red Devil TSP/90 Heavy Duty Cleaner, and when I got
home, I noticed it contained no phosphates.

Later I saw Tri-Sodium-Phosphate itself for sale.
Which cleans better?

I ve always stuck to the real stuff. I use it to soak my hot tub filters
and to get grease out of jeans

Are there other reasons for using one or the other?
The fake stuff is "kinder" to the environment..no phosphates