Look, there were only 48 Ethervoxes made, total. The Etherwave Pro is a relatively new instrument, it's only been around for a couple of years. Prior to its appearance on the market, aside from the 48 lucky people with Ethervoxes, a "pro" thereminist looking to buy a new instrument had few choices... they could spend a large amount of money to buy an instrument directly from a very small manufacturer such as a Tvox Tour or a Wavefront (both of which are reputedly excellent, but many people feel uncomfortable spending large money on a relative unknown), or they could buy an Etherwave.
If you're asking if the Etherwave can be played to a professional standard, yes, it can be and has been. If you're asking if it can sound as good as a pro model, that's strictly a matter of taste - in my opinion it can, but my opinion is meaningless to you in that regard.
If you're asking if it's durable enough to be taken to gigs, yes, it is. Its cabinet is nice thick wood. The only problem I've had with mine is that the screws that hold the control panel in place kept falling out so I replaced them with nuts and bolts, which has worked fine, and apparently that's a unique problem because I've never heard of anyone else having that problem with their Etherwave. It's also nicely portable - I bought the Moog gig bag, and I can just sling it over my shoulder and take it anywhere, it's light and small enough to be quite convenient.
Seriously, I suggest you buy Peter Pringle's instructional DVD from http://www.peterpringle.com/ He demonstrates a number of instruments including his (older, built from a kit) Etherwave.
Also you might find it comforting to look at ebay and see what Etherwaves are selling for - they retain a lot of value, so when I bought mine I kept in mind that if I didn't like it I could always sell it and get most of my money back.