I don't know if anyone has intuitively solved a teraminx before. I think that someone could do it though.
I don't think that it is worth buying it. I've thought about getting one before. But I've also thought "How much will I use it?" While it probably wouldn't be easy to solve, I don't think that I'd solve it more than once or twice. I'd rather get some other puzzle that I haven't solved before that costs less.
I think that the best brand is mf8. In this video
by blizzardkb, he compares the two different options. (There's also an addendum