Welcome fellow Soma cube puzzler! I remember the Soma cube craze of the 1970's. It's been mostly forgotten after Rubik's craze of the 1980's, but the Soma cube is still a great puzzle.

I just brought of of these for a friend. At 3.8 cm, it half the size of your puzzle. I haven't seen it yet so I don't know if it's too small. Besides the normal sized one like you posted, I also have this one. The top doesn't fit on well, but it is a good size, and I only use the bottom box anyway.

I'm sure you know that there are 240 unique solutions to the Soma cube.

Edit: Thanks for the head's up on the Dee puzzle. It's more like a super Soma cube. I need to get one.

If you like the Soma cube, you might also enjoy the older flat version, called Pentominos.
And then there is the cross between the Soma and the Pentomino, called the Tetris cube. It almost as fun as the Soma. There are two different Tetris cubes out there. This is the one I like.

Problems worthy of attack
prove their worth by fighting back.
― Piet Hein, inventor of the Soma cube.