Naveed,
I think it was you who asked:
"don't you agree that a one antenna (pitch) theremin would be an excelent beginners learning tool?"
The answer to this is, in my opinion, a firm 'no'. I have an Etherwave Pro now, and even though I can play some rather challenging pieces on it, I still am unable even to play 'Mary had a little lamb' on my first space-control box, which was a $40 bought from Ebay. No amount of practice will be able to correct this - the instrument itself is inherently not designed for precision theremin-playing. If however I had wanted a cheap box to make woo-woo noises with, then that theremin would be perfect. There's no need to buy a Ferrari if all you want to do is get from point A to point B. If on the other hand you want to drive really, really fast, or do something impressive, then the situation is quite different. These machines are not THEREMINS. They are, TERRORMINS.
Believe me, practicing on a terrormin will give you no advantage when you get a theremin. I know it sounds dumb, but it's the honest truth. It's like trying to start learning to play the piano on a table or something. :)
My advice = GAMBLE! You have nothing to lose and everything to gain. Etherwaves retain a huge percentage of their value, and most stores offer a 30 day returns period at the very least. I'd advise you get an Etherwave, as I cannot comment on the quality of any other theremin. The Etherwave is fantastic. The Pro is better, but not really five times better as the price would suggest.
