Whether the results are good or bad might depend on the data? How well it predicts the bandwidth? Relatively speaking I would say IBK is giving you much better results than Linear Regression. Better correlation and lower errors. Have you tried varying the k value number of neighbors? There are other classifiers that can do regression, SMOReg is like SVM for regression if I remember right. You could try a few others, this might give you something to decide which gives you best results.
Whether the final errors are acceptable might be up to you.