That the frequency response is not neutral in the top of the spectrum, with +2.5dB@10kHz and +5dB@20kHz. This shouldn't really matter in a guitar/bass soundchain for which ultimately the speaker/cabsim/IR will filter everything after 5kHz or so, but in case we plan another use for it... And I think this is linked but there is a little more noise added in neutral than the Joyo for example, and the 16kHz band does weird stuff with noise and saturation/crackling when increased significantly... Overall for the price this is a good product that does the job in a instrument soundchain, maybe the slides don't look as sturdy as the joyo also...