Since I'm designing my own system (yet another one, but years in the making), I've read a lot of systems, yet this one is so straight forward and well written - its concept is plain fun but the maths are a bit odd.

Chance of success without Focus

• Disadvantage: 33% (-23%)
• Normal: 56%
• Advantage: 70% (+14%)

Chance of success with Focus

• Disadvantage: 50% (-25%)
• Normal: 75%
• Advantage: 87.5% (+12.5%)

So, I use a single d12 instead (+2 if Disadvantage, -2 if Advantage, -1 if Focused)

• Disadvantage without focus 9+: 4/12 = 33%
• Normal without focus 7+: 6/12 = 50%
• Advantage without focus 5+: 8/12 = 67%
• Disadvantage with focus 8+: 5/12 = 42%
• Normal with focus 6+: 7/12 = 58%
• Advantage with focus 4+: 9/12 = 75%

And complication is on ones!