The straddle set up was a bit of a ***** to get setup.
Basically I just wanted to get around the seat tube and have a short straddle.
It took a bit of fiddling, but turned out pretty well. It offers as much of a mechanical advantage as drilling through the seat tube, only looking more industrial.
I made the 2 triangle plates, and used 6 pinchbolts (with nyloc nuts), and one straddle cable hanger, and 2 spokes.

https://static.flickr.com/30/47857638_9cca49842d.jpg

Thsi is the grind plate.
https://static.flickr.com/31/53086688_161c3b0f1c.jpg
It has flipped over on me, at the worst possible time.
I lost my footing on a rollout, and dragged the foot, and when I climbed back onto the pedal it was already the right way around.
Basically its weighted to always face down, but that doesn't apply when the bike is weightless.

so would you recommend the pedal plate thing..?

and do you think that i would destroy my aluminium Primo hollowbites riding street...or should i just use the pedal gaurd for park..since i have aluminium cranks..?

Hey, that's a pretty tight brake set up. Does having a short straddle increase the braking power by much?

I wouldn't. I ran one of those for a while, and it really doesn't help very much. You grind slower, all the hits to your pedal still kill the bearings, and it's more slick if your foot lands on the wrong side of the pedal.