Filament or settings ???

[TKTrooper 0]

. Hi all, I am having a nightmare printing with the mattforge filament. My prints seem to be very weak and brittle. Now i dont profess to being an expert, i am but an extreme novice who prints for mine and my daughter fun as we like to print and paint models together. So any conclusions expressed are based mostly on pure observation. But i wll include some pics to hopefully show what i am seeing.
Now the setting i have i have used over and over and had no problems with other filaments. I have printed the same models sometimes with different filament brands (often cheap ones) without any of the same issues, which is why i think the issue is the filament. However when i asked about this and showed pics on a facebook group people suggested the issue was either under extrusion and/or settings. i can see there are some under extrusion evident on some pics of a certain model, but i am still having issues on models that have no under strusion problems at all. I have changed the print temp between 195 (recommended ideal temp) up to 220 (which some said they had best reslts from for this filament) and there is no difference. I have increased material flow in 5% increments up to 115% and still no change.
As for other settings; as mentioned i am a complete novice and if i am honest dont really fully understand them so dont like to mess with them too much. But if the issue is settings can anyone recommend changes that might improve the situation?
What i am finding is that once printed, the model is very weak and brittle, it does not take much force to cause what ever the model is to fall apart, also the perimieter walls dont seem to be sticking together very well as you can also see in the pics. This seems to be the biggest contributing factor in the weakness of the model as once they seperate the who things goes to crap.

Again, i dont have any of these problems with other filament, only mattforge. I did contact them for advise and all i got was that it is under extrusion and to increase flow rate. Which i did to no avail