Realistically, an Open Degree probably won't end up as a totally random combination of modules, because most modules at levels 2 and 3 have some suggested prerequisites. You can, in theory, take whatever you want, but it probably won't go well if, for example, you suddenly decided to study Spanish at level 3 even though you've never done it before, or whatever.
In practice, then, most open degrees end up as either a combination of two different subjects, each of which is studied at all three levels; or as a pathway through closely-related subjects but with a bit more flexibility than within the equivalent named degree (for example, if there were two modules you really wanted to do at level 3 but the named pathway only allowed to to do one of them, you might pick an open degree instead so as to be able to do the combination you wanted). It's probably a good idea to check out the available modules and the pathways you might follow, to get an idea of what's workable.
In terms of jobs, a large percentage of graduate jobs are open to graduates in any discipline, so an open degree would certainly be fine for those. It's hard to answer regarding career plans you aren't sure about, obviously! Some fields will want to see a degree in a particular subject, others aren't at all bothered.
Personally I think explaining an open degree is perfectly straightforward - "I have an open degree; I studied a combination of Creative Writing and Design & Innovation". Job done.