Sounds Benford-y, yeah. The biggest relative "error" in [0,99] is going to be at 19, where the estimate (1 * 10^0) at only ~52% of the actual value (1.9 * 10^0). That local minima for accuracy recurs at 199, 1999, etc. From some quick spreadsheet-fu, the mean underestimation for [0,9999] is 88%.

Meanwhile, with the "teens" trick, the local minimum is 29 (68.9%) and then at 299, 2999, etc, and the mean underestimation is boosted to... huh, only 91%?

Then again, I'm assuming a completely even distribution, which probably won't be true in some contexts.