@bluenight setting aside all of discussion of how streames sound there are two basic factors that decide about stream quality IMHO: if it works flawlessy supporting all the formats and inputs/outputs/connections you need and user expirence. I would also consider how much time you need to put into setting up correctly as optional third.
In all those 3 areas Lumin U1 Mini shines for me. I've plugged into the network, conned usb stick, installed mobile app, setup streaming account, connected to the dac and started listening.
In the past I had similar expirence with mconnect based Mytek Brooklyn Bridge while IMHO mconnect app could learn a thing or two at least from Lumin.
I have exactly opossite expirence with zen stream. The software is in constat beta. In fact to enable some features being advertised by ifi as available you must install beta firmware. Up to this point it never played DSD256 files correctly but other users reports it works. Not fo me. Volumio UI is light ages behing Lumin. You can bypass it using Tidal or Roon for example however I am not Roon user and for me the whole idea of streamer in audio chain is to be able to remove any pc from it.
In summary: be very careful when you select streamer. I am so glad I've got ifi zen stream. It showed me how brilliant job both Lumin and Mytek done.
For me zen stream is like Chord poly: if you get it to work you may love it, but there is a chance it will not work and then you will hate it.