Ill counter the above and say that the boss sounds fine, Ive had mine for a while now and dont notice any loss in tone at all. You have to set it up but that takes what....30 seconds?
I like the Boss NS-2 but have never tried the ISP. I have heard it is better. As for the boss I have mine set up right and have no problems. If I am picking light with the volume of the guitar down I turn it off other than that no problems.