So much choice! But then a decision has to be made!

Length

In simple terms the size of your work is going to define which length version is most appropriate for you. If undecided between two sizes then it might be prudent to pick the larger if you have sufficient work space. The lengths match the standard sizes as follows:

for A3 - Mini
for A2 - Midi
for A1 - Plus
for A0 - Maxi

Duo or Trio

Again simply put, if you are a photographer or if most of your work is the same size and typically mounted in windows of the same size then the Trio's parallelogram would be an advantage, both in marking out and cutting the windows.

If your images are all of various sizes and vary from mount to mount then the Duo would be the correct choice.