I hope the coaster brake isn't like the ones from Shimano. The coaster brake bikes I had in the past scrubbed off way too much speed. One bike I had (Bianchi Milano) got sold because it would lose momentum. I purchased a 20 year old hybrid that had a much better freewheel. Someone also pointed out there's something about a coaster brake hub that creates a huge amount of drag.

My second coaster brake bike (Dahon Presto) is collecting dust this very moment. It also suffers from the same drag problem.