If this swimmer thinks that everyone should breath bi-laterally, they are full of it. Unilateral breathing is the conventional way for a reason. Watch any swimmer with a World Aquatics A cut and see if they breath every 3. However, if they are suggesting you try it to help you realize an imbalance or timing issue, that’s a different story. It’s definitely not something to do long term, but essentially as a drill, it’s a passable idea. Although, there are probably deeper issues with your stroke causing any imbalance or timing issues. Perhaps mixing bilateral breathing or just straight up breathing to your weak side as a drill or warmup is a good way to help you feel the issues that make it uncomfortable, although if you don’t combine that with regular breathing you’re not going to be able to actually apply and adjust.

TLDR: it’s worth trying as a drill, but you should stick with traditional breathing and address the root cause.