hi just to share with you:

I have been using 3-5-2 flat for few seasons. I say it works well for my team so far as for style, normal mentality, mix focus, short passing, normal tackle, own half pressing, zonal marking, counter. No red or blue arrows.

I think opponent find it difficult to break down possession against me.

If the opposite team quality rating has more than 5 points against you, I think this formation may not work well.