Can anyone explain the differences between Duo (sub)models?

So I have the regular DUO which I got for €65, I think that is the simplest and oldest model, if I am not mistaken?

IP-DUO? But then in many videos I see a very similar one with the model name IP-DUO What does that stand for, what are the differences?

DUO-PLUS, how is that one different from regular DUO

Afaik, none of the above have a different venting system, with extra button or such. Then I have seen at least 2 more submodel DUOs that look extremely similar to the base model, at least on quick glance.

Then there is the Duo Gourmet, that one does seem to have different display, different venting part and possibly more functions... ?

Can anyone make sense of this or is there a list comparing them all?

Thank you. :)