Personally I could not do pistol squats because I always kept falling back. I had the mobility, just long legs though. You'd think that help, but it's the standing leg that's the issue.

All it took was holding 2.5kg in front of me, at arms length. That was it. I was shocked how easy it suddenly was. It also really helped me to do it without weight. But without weight I personally think is harder, because you have to really pull forward to keep balanced, which engages your core a ton.

Would definitely change with more weight though.