I found a couple (below), but the island reconfigure was part of a bigger reno so your friend's DH might not consider these to be a valid comparison. Best would be if your friend uploaded some pictures of her kitchen and asked for ideas. Do they have a cooktop on their island? That may be a case for keeping it as 2-tier.

I've had 1-tier and 2-tier, and I prefer 1 as do most people I know who have done renovations (many have gone from 2 to 1.) I like the bigger workspace, more comfortable seating (and I'm tall), and I feel like a pretty counter stone is more visible on a 1-tier.

Search different terms under "Discussions" and you will find some old posts showing photos.

Here is one:

https://www.houzz.com/discussions/5689944/kitchen-updates-two-tier-angular-island#n=30

I found some before and after pics online for you. My experience:

Lowering counter pros: Larger counter space, more room for cooking, more inviting for people to sit and eat, stand and socialize.

Lowering counter cons: Cannot hide kitchen mess from view. Harder to keep guests out of your workspace. Might need to rearrange electrical outlets. If you are not doing an entire kitchen renovation, could be like picking a thread on a sweater that unravels into a much larger project.

Thank you, this is so helpful! Maybe my brain just wasn't coming up with the right search words because I kept coming up with nothing LOL! Appreciate your help!