I haven't done Non-adversarial justice. From the looks of it, it's probably on the easier side of elective law units, as it doesn't look like hard black letter law, and the assessment consists of a take-home exam and an essay. That said, the readings may still be moderate-heavy. If you excel at units that involve policy moreso than 'problems', it's probably a good choice. Not sure if Ross Hyams still takes it, but if so, he's a great lecturer.
That said, 3 core law units in a semester is a tough workload by itself. I'd be concerned about the plan as it's likely to create a pretty hectic exam period (especially as there's potential for all 3 of those units to be held early on in the exam period, given the bigger units are regularly scheduled then). Once you throw in another law unit, the workload becomes noticeably less manageable. Personally, I would be inclined to pick a soft first year com unit, or do only the 3 cores. If you can do that and push back a unit for a summer or winter semester, I'd definitely consider it; your choice depends somewhat on how feasible summer/winter units are...