I have and use the Gold Cube and to me it is well worth the money.
It does not sound like this would be the best tool for you however. The Gold Cube is a great concentrator. You still need to pan those concentrates to get your gold. I deal with very small flat gold that is easily caught in the second tray of the cube and I get a very small amount in the third tray, maybe 5% if that much. The first tray is just a slick plate and does not hold the gold I find. For the material I work, I do not think the fourth tray is needed or the cost justified. Depending on the material you are working the fourth tray could be worth while. The first several times I ran the cube I reran the material and did not find a speck in the tailings.
Work on your panning skills before spending the money. Practice, Practice, Practice. Jason has great advise on the classification and use of bbs. I even used number 7 and 9 birdshot to work on technique when i . I also like to use magnets to get rid of my magnetite, but be sure to keep these as small gold can be caught up in the sands.
I personally do not try to get every speck from my black sands any longer. I am gathering more material and saving the concentrated black sands until I have enough to justify talking my wife into letting me buy a set of good classifiers and the blue bowl. Since I have not only a wife, but three kids and a granddaughter, I will need to show the gold found justifies the money spent. That means cashing in some of my stash and ordering them AND being able to hand her at least a couple hundred bucks or other creative means. I was able to get both the Gold Cube with an #8 Classifier and a Royal Drywasher this summer as "gifts" doing odd jobs for people and instead of letting them pay me requesting the equip.
From what I have seen, the Blue Bowl does eliminate the need to pan your very fine materials but is also slow and requires a lot of patience and very careful classification. I still plan to pan my material and then use the blue bowl to catch the -100 and -200 material I am currently letting slide.