I'm using this currently to reamp guitars for our first album. Instead of spending money in the studio waiting for the perfect take, we can pre-record the guitars using a DI in our rehearsal room and if we want to tweak a tone, use the studio time to do that.
I'm currently using it on the flat eq setting and yes it does ever so slightly, almost imperceptibly, effect the tone, but it's a nice sound - it feels warm and rounded like a nice preamp. It's completely unnoticeable as soon as you use any effects on the guitar and to be honest, if you're reamping then you're tweaking the tone anyway. I haven't had a chance to try it on bass yet, but I assume that's where perhaps the low pass filter would come in handy.
It's also allowed me to experiment with using my guitar pedals as vocal effects units as well which is opening a world of possibilities. I sometimes feel the plugins in DAWs are a bit sterile, or ludicrously expensive but I've spent hundreds of pounds on guitar pedals that have incredible sounds, so now I'm able to use them to achieve the sounds I want.