I am thinking why (besides Chromecast which is nice) I should buy this and not Allo Boss2?
Chromecast is one of the main selling points of this device in this price range, it's not a 'besides'. Comparing it to the Allo Boss2 is therefore not useful, they are apples and oranges. Either you are looking for a streamer with Chromecast and this device or the NP5 (at more than twice the price) can be interesting options for you, or you don't need something with Chromecast and the Allo can be an option. It's as simple as that.
Another big difference is ofcourse that an Allo Boss2 is user-managed, you are responsible for it's OS and software updates etc. Things like Spotify or Tidal can stop working at any time, since they are using open source implementations. The SOLO is manufacturer-managed, it's plug and play and receives automatic firmware updates. Two very different approaches obviously.
My dac is chord mojo. I am satisfied with its sound, but it is quite sensitive to the source and type of connection.
I'm wondering why Solo and not Prisma NP5?
I'm wondering why the Chord Mojo? Perhaps you should just get rid of that if it's so sensitive, instead of focusing on what reclocking can do "in theory".
Good DACs are transparent anyway, you're not going to gain any audible improvement by using a Chord Mojo instead of the internal DAC of either the Solo or the NP5.