Has anyone ever had success with Gentle Sleep Training (or No-Cry) methods?

My LO is almost 5 months. His dad is very against CIO, even though I've tried to explain it's not harmful, he just doesn't feel confident with it. I want to respect his wishes so I've been trying to look into gentler methods, but all I ever hear about is how they've failed and parents had to swap to CIO.

I was just wondering if anyone ever had a positive experience with gentle sleep training and have any tips or recommendations.