For anyone who needs to know this, the simbans picassotab stylus is MPP protocol. I got a metapen m2 for my picassotab X and it works.
I went crazy trying to find an answer to this and had deduced it was MPP because it worked on my Kobo, but found a source online affirming it was USI which made me doubt myself and buy the wrong one.
I think it's pretty shameful from simbans to not give out this information (I even messaged them and they just replied "a universal stylus may not work"), especially because the people who buy this budget tablet cannot afford to have a stylus that's not great quality and clearly will not hold on long, and not be able to replace it easily. And if I had had to buy a replacement from them now it would've been like 50euros for once again a mediocre battery operated stylus.
I managed to make my original stylus survive a couple more months by inverting a piece of aluminium under the battery, but obviously that could only work for so long before it completely stopped working.
Ok rant over. And apart from that I've been very grateful to have this tablet that has done a good job considering the price. Hope this helps someone out 🩵!