I got the Julianna to use with synths. I mainly use it with Dreadbox Nymphes and Arturia Microbrute which have mono outputs and I love how it widens everything so pleasantly but it doesn't loose any of its energy even in mono mixdown. The fact that it can do mono to mono, mono to stereo, stereo to stereo makes it really versatile. The effect can be subtle or wild. The feature that really got me by surprise was the tap tempo, it's super useful, especially if used with the random LFO wave. I love the hidden LFO drift function, it sounds lovely on pads and strings.
The lag knob and the DCV knob are also game changers, you can make really unique chorus sounds.
I have never used it on guitar but we tried it on electric bass and it was delicious on slow tunes with slow rates, but that's obviously a matter of taste.
It's really easy to dial in a nice tone but the hidden features can offer way more complex sounds, it's up to you.
It's really solid in terms of construction, in its metal case with sturdy knobs.
I am really satisfied with it, the only things that bugs me a little is the bump on volume when you turn it on, but it's not that big of a deal.