Please read the
'Informative posts by Rob Watts' section of
post #3. I've included loads of discussion, there, that will help in your understanding.
It is true that Mojo uses fundamentally the same technology as Hugo, and is very keenly-priced, considering how much leading-edge DAC technology it incorporates.
Mojo has approximately the same power output as Hugo, and approximately the same complexity of digital processing, but it is tuned slightly differently. Different people will hear the differences differently. Personally, I hear Hugo as sounding slightly more 'airy' than Mojo, but the differences are quite small.
Hugo offers fullsize RCA Phono connections, which Mojo does not. Hugo also offers 1/4" headphone jacks, while Mojo has 3.5mm (1/8") headphone jacks. Hugo has galvanic isolation, while Mojo does not. And there are a few other small differences (Mojo can accept extremely high sampling rates, but almost no one would be able take advantage of that, on the move, due to limitations with portable transport devices currently available).
I'm sure John Franks or Rob Watts will chip-in, if they see-fit, but my understanding, from various interviews I've encountered, is that, following-on from the enormous success of Hugo, the Chord team wanted to get the same fundamental technology and performance into the hands of an even wider audience, and to do that, they had to create something at a much more-accessible price-point. The rationale behind this was (partly) because they wanted to lift more people into the hi-fi realm of portable listening, and thus enjoy their music more than they can from many of the mp3 players and smartphones available in the past few years and present day. Bringing more people into a realisation of how much better music can sound, on the move, when reproduced to a high technical standard, may benefit not only the customer and the company, but, perhaps, by virtue of expanding the industry customer base, the industry as a whole.
I admit some of the above sounds a bit like advertising copy, but it's simply the most succinct way I can relate it to you

You can find the specifications of Hugo and Mojo
here
.