The attached IMGUR album shows all: http://imgur.com/a/OSVjK
I can't paste the images here directly, they are too big. You wouldn't see the detail at only 800pix anyway.

The model shown here is typical of the work we do - architectural models.
In order they are:
1. Slic3r 'basic' interface. Clean, simple. Press 'Export G-Code' to get your output. You can even do 'drag-and-drop' instant output.
2. PREVIEW MODE - this is the most important feature! External shells shown yellow, infill in pink. You can see exactly where plastic will be laid.
3. PREVIEW MODE - Layer by layer! This shows an area where this VALID file is producing some weird shapes. This print will FAIL. It's nice to know this before you print!
4. Plan view (preivew again!) of that area of failure - note the triangluar 'hole'. This is likely an interior facet, even though every STL checker I used says it's valid. Even Up 2.18 said no errors.
5. Print settings. This could be facied up with little pictures.. but it doesn't need it
6. Filament settings. very simple. Note temperature control! Very important - especially the first layer temp.
7. Printer settings for my Flashforge Creator Pro (Sailfish firmware)
8. Slic3r has two modes - SIMPLE for 'just print my job' and EXPERT for 'I know what I'm doing and I have a tricky shape to print'
9. Expert mode Support settings -far more detail than UP 2.18 & Up Studio
10. Preview mode showing 'Pillar' support mode. Support shown in green. Note 'messy' support around the failure area - this print would probably still fail!
11. Changing the support mode to rectangular neatens up the failure area. To my eye, this print would probably work, although at the expense of some fiddly support removal.
What all these images indicate is the importance of the PREVIEW mode, and the importance of detailed control of print settings. This is not to say there can't still be a 'simple' mode for 'it just works' printing, but the detailed control is vital for professional work.
Given that a trial of the UP software wasn't possible before purchase (download required machine serial number) and given that the Up software is the only way of printing with the Up Box, this is a major problem! A FREE piece of software is VASTLY better than what UP provide.
My suggestion is to not bother trying to recreate what Slic3r and others such as Simplify3D have already done - just allow the Up Box to be able to print the G-code output from these other applications. Continue with a very basic tablet-like application by all means - it's probably very useful for younger users, but for professional users PLEASE allow the use of 3rd party apps instead of Up Studio / Up 2.18