Ok - I just saw this post.
Sorry that you didn’t get what you’d hoped. From what you describe, I think the loose screws you mention are the adjusting screws that set the free floating caliper in relation to the disk. I think you may have the same brake, and perhaps same bike as me. Did you get it from a guy in Wembley? If so, it is normal to have two adjusting screws that are only finger adjustable. It is meant to be like that.
To set up these brakes, you need a piece of white card and good light level. If you up-end the bike so the wheels are in the air, you can put the card behind the caliper and you will see how much gap there is between the fixed pad and the disk. The fixed pad is the one that doesn’t move when you push the lever on the caliper to engage the brake. One of the ‘loose screws’ moves one end of the fixed pad nearer or further away from the disk and the other moves the other end.
I set mine so that there was a narrow gap and that the disk was almost not ever touching the fixed pad and when it did (because the disk is not perfectly flat) it only touched it with the merest touch. You should make sure that the wheel can spin pretty free, but doesn’t leave a big gap between the fixed pad and the disk.
Now - this next step REALLY IMPROVED my brakes.
I took a good look at the other pad - the one that isn’t adjusted by the ‘loose screws’ as you call them. On my bike there was a pretty large gap and the braking was vague and spongy. I took the allen key and loosened the screw on the brake arm that clamps the cable to it. I had already made sure that the adjusters on the brake levers (handlebar ones) were screwed pretty much inwards. Now, I used my hand to pull the brake arm on the caliper so that the brakes were almost applied, pulled the loose cable through and nipped up the allen bolt again, but just lightly. Then I spun the wheel and checked that nothing was dragging. After a couple of goes at this, I got it so that the clearance between the disk and the moving pad was just about perfect - not touching anywhere as the disk rotates, but no big gap either. This adjustment is really just shortening the cable. Then, I tightened the allen bolt to secure the cable. This is VERY important obviously, you don’t want to grab a handful of brake in an emergency and find the cable pulling through, because you didn’t tighten it, but also you don’t want to overdo it and strip the small threads either.
My brakes are VASTLY better now. Not spongy at all, and the back wheel will lock up if I grab it hard. I use bother brakes lightly and have very good stopping power. I love these brakes now.
NB>>>
Beware over enthusiastic front wheel braking. You can easily go over the bars if you yank on the front brake.