The nice thing about the FV-1 is that the audio DAC, ADC and pot interfaces are part of the chip. Simple and compact. But the Wavefront part is more powerful. I've written some distortion algorithms that use nearly all 1024 words of instruction memory - there's no way I could use the FV-1 for this application (non-linear wave shaping with up/down sampling and tone filtering).
I've made a few of the 10-pin boards shown on the website so far. I'm almost ready to ship five more. Three people have emailed me about them. I've agreed to send them out for free just to get them in peoples hands in order to get some feedback! You can have the other one if you want it. The only downside is that it's taken me a long time to get these done since I'm busy and I don't like soldering

If you want it then email me your address and I'll ship it out there.
I should have one more available after that - if someone wants it send me an email.
With the info on the website anyone should be able to build one of these boards but it obviously takes some work (order PCB's and parts, solder, burn firmware, etc). The files are out there. If I had more time I'd build a bunch and start selling them for $30 or so. That was the plan but I haven't been able to scale up to that.
Yes, any USB to serial converter/adapter will work as long as the adapter has a driver that creates a virtual COM port. All board's I've seen use one of three IC's as the USB/Serial converter. Most are either based on an FTDI part (FT232 or similiar) or the CP2101/CP2102. All of these have the appropriate drivers for Windows, Linux and MacOS.
This next rev of the board omits the CODEC so that people can choose their own CODEC and even use up to four CODEC's if desired. It's easier to assemble too. If there's enough demand then I'll build more 10-pin boards that have the WM8731 codec, otherwise I'm going to phase that board out in favor of this 16-PIN DIP board that omits the CODEC. The long term goal is to build these this summer and sell for about $20.