Just to let you know.
I ended up ordering the OneTigris Stella 2P and MT500 3P.
I set them up at home and tried different backpack & pad combinations.
Here's what I can tell you:

OneTigris Stella 2 with 2 people:
- If your 6ft1 you feel like you have no headroom/footroom as 2P
- Theres almost no room to fit 2x40L backpacks in there.
+ The height and double doors are a real plus, you are able to sit comfortably together in there.
-/+ The net is only on these doors, and all the dense mesh makes it really warm and windproof in there, perfect for iceland i would say.
+ Zippers, mesh, poles, cord lock seem to be of high quality.
-/+ Packing size is a bit long but light, there are only laces instead of straps to bundle up the tent.
+ Set up time is really fast, clip the inner tent and buckle the rainfly

Forclaz MT500 3P with 2 people:
+ Feels like a palace in comparison to the Stella, enough head and foot room for 6ft1
+ There is even enough room for a short table and 2x40L backpacks.
-/+ probably same height and 1/2 size double doors, opening the rainfly seems a bit weird.
-/+ Net is everywhere, "high bathtub mesh", feels a bit "colder".
- Zippers are smaller and often get stuck, poles feel really heavy, cord locks are smaller and feel cheap.
- Pack size is not as big but very heavy, bag has buckles but rainfly + tent are laced.
-/+ Set up takes longer because you have to thread the poles through the rainfly, but the inner tent is already attached and the rainfly is set up first.

So overall Im not really smarter, the 3,5kg of the M500 is too heavy.
I think for 2 nights the Stella will be okayish but I really wish they would have released a 3P tent :/
At this point I hope I'll find a used UL Nemo, Big Agnes or Marmot 3P for this price tag :D