If you weld all day then you know why the Torklift mounts cost $700. They are well made and actually they make them to order often in order they don't have hundreds of different configurations collecting dust on the shelf (different brand trucks, different years all need different designs).
I am no pro welder, but came close to making my own, but opted instead to use the Torklifts. I have no regrets, though I typically do like to DIY for most everything.
The "cuts" or slots could be just the continuous cutting byproduct, but my theory is that this is a built-in weak link. Given enough tension this part might bend and let go before other components break. I could be wrong, and some TCs might have very weak toe-down points on the camper which would break first. You never want the truck frame to be the weak link.
Building these yourself often results in over-built, very strong braces, which could bend or damage the truck frame. I think most drivers would prefer the TC just fall off rather than anything on the truck become damaged.
Your Fastguns were a good choice.
A key thing to keep in mind is that the tie-downs (chains or Fastguns) oppose each other front to rear, where one chain pulls the TC forward and the other pulls the TC backwards. This balance of fore/aft tension helps keep TC in place and prevents it from sliding forward when braking or rearward when accelerating. The tie-downs should make and angle, not just route straight up and down.
Yes, the front of the truck bed will stop forward movement, but the bed is not necessarily made to hold a TC in place like that, better for the chains to hold it.
