I have owned and operated skid steer loaders since 1975. I have operated them with snow buckets, plain edge digging buckets, grapple buckets and forks. I've also used hydraulic post hole diggers and rear mounted scarifiers. The 1840 Case in that video is very familiar to me as we've owned about six or so of them and we still have the 1845 which is the bigger brother of that series. I can't say that I'm particularly impressed with what I saw in the video. The tree stump selected for removal had been dead many, many years. I could have popped that sucker out of there just as easily with the forks. The same holds true with placing rocks or boulders. The forks are amazing once you know how to utilize them. I just don't see this spade as being beneficial for those operations.
Now, for digging holes to plant trees, then this might have some positives because it removes more dirt from the hole than what the forks alone would. All the same, it's slow compared to a post hole auger with a proper tree auger on it or using a tree spade. As a trenching device, it is also painfully slow and messy. You will rip the crap out of any lawn whether you use a two-wheel drive tractor or a skid steer. You are far better off with a Mini-EX on tracks or a Ditch Witch style of chain trencher. In all fairness, could this thing solve the odd problem rather cheaply? If you only had six small trees to plant and the tire skid marks didn't concern you too much, then it would likely work OK in decent ground. Did you notice that all these demos were done in soft, loamy soil that was deep? Is there a reason why they did not show you how well it works in hard, dry clay? Figure it out.
There's a reason why Case offered the 644, 646 and 648 models with a backhoe.
The site does not tell you the cost of this device and that annoys me. They only show it in combination with a skid steer or a Compact Utility Tractor, both of which outweigh and have more HP than your 444 does. Without the optional fork attachment for your loader, you would be limited as to how deep you can dig. I'm not sure that you can move the forks that close together on a 600 series. Perhaps if you told us more about what you are trying to do with the 644, we might be able to advise you better.