I bought couple and yes, they are impressive, but I wish they didn't make them out of metal. Like Daniel mentioned, the painted metal surfaces aren't as nice as the surfaces on the European buses. The engraved lines seem not as delicate as in the plastic buses and the very glossy paint is applied in a very thick coat. Just like the metal CMW vehicles the metal areas are somewhat crude and lack the finesse of fine all-plastic N scale models.
Only the bottom half of the models is diecast - the upper part (with the windows) is made from clear plastic which is then painted.
I was impressed by the fact that the side mirrors are made from some sort of flexible (vinyl?) material, so they will be very robust. They do have reflective mirror stickers applied, but those are not glued on very well.
The clear plastic window areas are painted on the outside with glossy transparent tint, with the window frames then printed over the gloss tint with satin finish paint, so they stand out nicely. Extra credit to Iconic Replicas for leaving the windshield and front windows clear.
On the light colored buses (like the MBTA yellow stripe bus) the insides of the wheel wells are white which looks strange. A quick coat of black paint will fix that. Also the axles have too much play (they can end up not properly centered in the wheel wells), but can be either shimmed or glued in place.
Even if these aren't ideal, I'm still glad to see models of modern buses available in N scale.