downforce without drag is impossible, that's just physics. changing the flow in and under will reduce drag and have the opposite effect.
here's an article that sums it all up nicely.
https://nasaspeed.news/tech/aero/ai...ases-lap-times-and-isnt-that-the-whole-point/
these panels you are all looking at I can't see that they'd do much of anything unless they are in fact reducing drag by increasing flow, which in turn will theoretically reduce grip and also improve economy. I don't think i'd bother with them myself unless part of an overall change to the aero of the car. so you'd probably want a wing that can give you some downforce back and maybe a front splitter as well.