I say go for it!
I have built many from hand because of necessity, while sometimes using a prebuilt worked fine.
If a prebuilt works for you, I say go for it.
If you have some custom needs, then may be better to build yourself.
But different brands I have used in past were fine and a time saver.
I've never used one---It seems to me that the flange would cause a bulge under the Durrock and make for a difficult tiling job. Also---waterproofing would be needed where the plastic pan meets the Durrock---
I build my own and waterproof them with Hydroban----
New members: Adding your location to your profile helps in many ways.--M--