The probabilities are identical to just rolling 1d6 vs. the difficulty directly, with one minor difference - in Cypher system’s way, you can fail at the difficulty 1 task 10% of the time (rolling a 1 or 2 on d20). The probabilities are otherwise exactly the same. Rolling a 3 on the d6 is exactly the same as rolling a 9 10 or 11 on a d20. A 6 is like an 18, etc. I guess the one other difference is that Cypher gives you extra benefits when you roll 17+ (tiers of critical hits).