You are right in some ways Nusbio and an Arduino with a UART, in term of features may not be that different.

With an Arduino specially Chinese Arduino compatible CH340 or with .NET languages you may be limited to 115200 bauds (about 11Kbyte/S) and you need to write and maintain a firmware. As a plus you get PWM and ADC. Nusbio1 can do between 15 and 28 Kbytes/S in SPI and there is no firmware. But there is no PWM. ADC or DAC are available as SPI extensions.

it is not a black and white answer.

But with the knowledge I acquired creating Nusbio 1 hardware and software, I am now working on Nusbio 2.

Nusbio v2 coming sometime this year will address some of these issues, IO default state as input, increase in speed transfer (I2C:Up to 128 Kbyte/S, SPI:Up to 2.4 Mbyte/S), 10 bit ADC, PWM. But unfortunately will be more expensive.

see https://twitter.com/MadeInTheUSB/status/848013033335029761

Depends on the protocol they use on the USB connection. Serial over USB has its quirks. Using a Leonardo, a Due or a SAMD21 based Arduino allows you to implement something like HID which should give you better latency

You are right though I do think HID is limited to 64 Kbytes/S. But an SAMD21 or 32U4 could allow me to build a cheaper product. I have to think about it now.

What I am currently achieving is

- 100Kbytes/S in I2C with a 10Mhz I2C EEPROM and - 2.4 Mbytes/S in SPI with a NOR FLASH at 103Mhz

using the FTDI FT4222 and the FT232H should the same or better.

what makes Arduino anything more than an open source Basic Stamp? I was using Basic Stamps a decade before Arduino came along. It's about choice.

I would think the fact that it is open source as you mentioned is the reason. My question was not meant to criticize just wondering if I missed something that makes these boards a better choice for an application I'm working on. I looked into basic stamp years ago also but the cost of them and my lack of funds at that time forced me to go down the PIC road instead.