A sliding table with miter fence is a lot better for doing angled cuts because it's mass is so much larger than that of a basic miter. The one I have really doesn't make cutting full sized sheets any safer or easier because it doesn't extend that far out of the front of the saw.
I have ripped down a few sheets of 1/2" ply into 5.5" x 96" strips using two in-feed stands and one out-feed stand. The only other two full sheet break downs I have done at home on the TS were cutting a sheet of half inch into thirds (16" wide each x 96" long) and I had help with that cut.
The better of my two table saws has a sliding table built into it. In the case of the Ryobi BTS-3100 (and BTS-3000) the sliding table is 1/2 to 2/3 the size of the add on sliding table BusyBee is selling. It doesn't have the telescoping edge support either that can be extended out from the left hand side of the miter fence, like the Busy Bee product does.
I watched the video for the one you were looking at and can't help but notice they didn't actually do any cuts at all during the presentation, let alone one with a full sheet of plywood.
When mounted on the saw it was designed for, the miter fence may well extend forward 50 inches from the front of the blade and allow the cross cutting of a full sheet. I still have to wonder about its stability when it is that far forward, especially considering a sheet of 3/4" ply weighs roughly 75lbs/30 Kg....
It would help to see the thing actually being used to take down a full sheet of 3/4, including the placement of the material on the saw before the cut.
I'm not saying a advertiser would forget to turn the camera on when two big guys were struggling to the sheet in place without tipping the saw over or marring the wood, but you know...seeing is believing...
I'm so puny I would have a hard time getting it up and over the fence without some scrapes..
It will be intersting to see if other members have comments about sliding tables. I know there is at least two more BT3k users here!