Hi Moriez
This comes down to personal choice and your intended use.
The Volumio Primo is based on an ASUS Tinker Board S SBC, based on Rockchip Quad-Core RK3288 CPU, to which Volumio has added an audio processing board. This is similar to the design of any streamer based on the Raspberry Pi, where the boards are not designed specifically for audio applications. In comparison the board on the iFi Stream is designed specifically for audio purposes, where the processing is done by an ARM Cortex chip, and is a later design.
Similar to the Bluesound Node, the Primo has an on-board DAC, so if you have an external DAC, you will be paying for something you might seldom use. One thing to check if you are thinking of investing in the Primo is the verson of the Volumio OS installed, which is now v3, and whether a power supply is included "in the box" (the manual states "Power Adaptor is optional, depending on the region and local seller’s policy"). The iFi Stream is purely a transport whereas the Primo is a music player.
Not sure if this helps.