An arranger is the combination of software and hardware..... if either one is still beta, then the arranger is beta.
I have no problem with the concept, and I believe that it is the way of the future. I look forward to getting one when the promise is realized, rather than in development...
For the high cost of one of these computer based arrangers, it should work as well OOTB as a comparably priced Yammie or Roland, but as of now, not only does it require a lot more money added to the cost to add the Giga and software instruments of your choice, but, as Domenik points out, you are relying on third-party companies to provide robust drivers to allow you to use the VST instruments of your choice in the Linux environment. Not to mention the debugging process you will have to put yourself through every time your VST instrument gets updated, or you upgrade the CPU or I/O options.
The future is coming, no doubt, but I don't feel it has quite got here, yet.
An arranger is just a tool. What matters is what you build with it..!