Richard Barry's FreeRTOS is certainly very popular and that is the main reason I ported it as an Arduino library. FreeRTOS works well as an Arduino library.
Personally I prefer ChibiOS/RT to FreeRTOS on the Arduino. It uses less RAM and the faster performance is not due to assembly code or tricks that make it hard port, it because of elegant design by Giovanni Di Sirio.
On Cortex-M I really like ChibiOS/RT. Giovanni's support for STM32 is great.
In short I don't think Barry's comments apply to ChibiOS. ChibiOS has many debug features, tracing, interrupt nesting, etc.
Both are good RTOSs. You need to choose which you like by using them.