Let's back up a minute. I own three T-8 class buckets, so I'll start first with my personal experience.
1. HD dirt/rock bucket with bolt-on teeth
2. Grapple bucket with bolt-on teeth that are much longer and aggressive than the dirt/rock bucket, and the bucket is the same size
3. Larger, light material (LM) bucket with no teeth
I haven't used the rock/dirt bucket in years now, it seems. The grapple bucket will do everything the rock/dirt bucket will do, and much, much more - including digging better in hard soil. The longer, slimmer teeth penetrate hard soil better than the short, wide teeth on the HD rock/dirt bucket.
The larger LM bucket is used frequently for hauling AND spreading loose dirt, gravel and mulch. You can back-drag with much better than with either bucket that has teeth. Being able to put down-pressure on the cutting edge instead of the rear of the bucket (as you must do if the bucket has teeth) allows you to smooth and even scrape much better going in reverse...
Be aware that bolt-on toothbars fit on and BELOW the cutting edge of the bucket, so it makes it even harder to backdrag smoothly than even a bucket with bolt-on teeth. (I've had both -- I had a bolt-on toothbar on my Kubota.) But, their long, aggressive teeth can come in handy when you want to scratch or rake off an area. I've raked the growth off my garden in the fall with my PT, for example, by back-dragging with the long, skinny teeth of grapple bucket -- then pick up a large pile of the stalks and carry them to the compost pile. When trying to do something like this with bolt-on toothbar, it is fairly easy to lose a tooth -- if they are the replaceable style. They're only held on with a small diameter pin (or bolt) and back-dragging is pulling against that pin. You need to be aware of that, and either carry a spare tooth, or to limit back-dragging.... (Done that too!)
So, my recommendation would be to not even bother buying the HD rock/dirt bucket. Instead, buy the grapple bucket (my most used attachment) or buy the larger LM bucket and put a bolt-on toothbar on it.
My two cents... YMMV