My only razor is an R106 which I'm quite happy with, but after seeing all of the glowing reviews for the '89 I'm considering picking one up. Will I notice any appreciable difference or should I save my money?
Someone with a lot more knowledge will need to speak to this but I think that EJ makes heads for Muhle or it may be the other way around. If you go to a web site that sells both razors and look closely at the pictures, you will see that the head of the DE-89 looks very close if not identical to the Muhle R89 and the R106. I think if you bought the DE-89 you would have a razor that would shave almost identical to your Muhle.
My advice would be to save your money and, not knowing what you're after in a new razor, go to a slant bar or perhaps an open comb. Maybe start thinking about getting a vintage Gillette?