We have them. We like them. I don't care for the look of recessed which looks pockmarked to me.

We used them in our brewery build out because we couldn't afford much else at the time. They are effective in the space. Maybe not the prettiest, but no one has commented on them. They are generally looking at the rest of the place and the beer menu :)

And, after a couple beers, they probably won't care at all anyway! LOL

They are great in commercial because they can be installed in fire rated assemblies much easier than recessed.

We have them some places where cans weren’t quite right but we wanted an unobtrusive fixture. i think they have their uses but don’t replace cans. It’s nice to see a bit of chrome on the outside in the bathroom etc.

I had not heard this fixture called a "wafer light". Halo calls it a "surface downlight", others call it a "flush or surface mount". The Halo SLD4 2700K is the best I've seen so far but because of the glare and diffused light I don't think its a substitute for something like a Lightolier L3. However, the SLD4 is much less expensive and easy to replace when it fails.

Halo 4" Surface Downlight

Lightolier Surface Mount LED

Lighter L3RD 3' accent downlight

Surface mounts are particularly valuable in challenging access locations, like a typical MCM home or vaulted ceiling, or a home trying for some type of energy certification that wants no holes in the ceiling plane. In a standard home, ICAT housings with good LED trims are going to be effective and inexpensive, and be less obtrusive, with less glare.

We used them in less visible locations. Pantry. laundry room, gas chamber, above secondary bath/shower ( I think - which shows how important those spots are - but we don't have glass doors there either).

On a top floor, they interfere with insulation less.

In New England I design a lot of renovations where the attic space is too valuable to be unoccupied or its used for HVAC ducts, etc. so insulation is added in the rafter bays and the attic/new living space is conditioned so air sealing of the ceiling below is not necessary. I believe this is beginning to happen in warmer climates too.