My thought on Prusa i3 (1) ....Structure stability.

Easy to built ... It is a big yes  !
Robust  .............No, can do better,

Let me talk about the MECHANICAL BUILT !!!?
If you look at the side view of the printer, you will know it is not stable. The vertical plate is only locked with M10 nut. It will FLEX .... The Extruder is providing a big moment on the structure, so it will have a clock wise moment . If your structure is not stable, the print out will be messy.

So some people added more structure to stablelize it. Like this.

Additional Rib to stablize the structure during printing.  In my case, I added  2 plates which I salvaged from somewhere to stabilize it.  Its free... 

Stability is very important . If you want better stability. Like this ... You can consider using Aluminium Profile 20X20mm Or 30X30mm. I seen Felix 3D printer used 40X40 mm profile. Like the Reprap wilson , 3Drag or even Felix .

Why is Prusa with Acrylic body or Aluminium plate not an ideal structure ?

What is a good structure for 3D printer ?

First, the body should not flex in any condition. Prusa Flex.... Mendel could be a better choice.

 

Second, the extruder exert a force and moment on the body. If it causes flexing it is not good.

Prusa has 2 supporting shaft vertically inline. It is not as good as Mendel where 2 shaft are horizontal. Of course it is easy to solve by making sure that you have additional support at the center of gravity.