I have the 5/8" thick one it has four tie down places but I only use 2. I think that's all that's needed. At least with the 5/8" thick steel you'll just have more steel to wear down and not that much more weight. It will be sturdier and your bucket probably won't be loaded to capacity when using the RR and a few more inches won't matter much. In other words I don't see any reason not to get the 5/8" thick one. Only reason I could think of would be if it was too wide to fit through some of the places you're working or parking. If you happen to buy a larger tractor in the future you'll be glad you got the large one.
I bought the forestry unit I think is what they called it at the time. It came with 2 ratchet binders. The ratchet binders with chains are recommended if your bucket is built heavy and sturdy with reinforcement on the top edge. If your bucket is a standard type that comes with most tractors its possible to bend the top of the bucket with a chain wrapped around it and using a ratchet binder. You can get the strap binder with cable attachments instead of the ratchet binders which might suit your bucket and you'll have no problem with that.
If you decide to go with the 1/2" thick you'll never wear it out anyway and it works the same. After you get it, use it like they suggest and it works great. When pushing forward into briars or brush kinda level your bucket with only the bottom teeth touching the ground then when backing out roll your bucket forward until both sets of teeth are touching the ground at the same time then pull the brush out. When pushing to make a pile just level the bucket back out and let the bottom teeth be close to the ground so it'll gather all the brush you've already pulled from the ground.
Mine is used a lot and it's one of the most useful tools I have. Can't dig with it though. Either one you get you'll see you got your money's worth quickly. Decisions ... Decisions :confused2: