I'm using my H9 in my guitar rig and have not noticed any problems. Now I'm exprementing with a setup for my bass and now there is a common problem. I always split my bass guitar in two halfs. One straight di-boxed "Clean" sound to the PA and one "Dirty" efx/processed sound. The "dirty" signal goes through the H9 and, guess what, the tiny litle latency the H9 have, has suddenly becomes very pronounced in the lower mid range ( a.k.a. 800Hz ) and two perfect sounding sounds has becomes unusable together. This is not a problem if you have a digital mixer. It's really easy to change the delay a litle bit for the clean sound, but if you are stranded with a analog console, then your f***ed.
The H9 have stereo in/out, as a bass player I'm only interested in mono efx but would be more than happy if the other channel offered me a "latency" align delay line as the only efx on that channel so I can run my clean signal thru it before the DI-box. In this case I would be able to adjust for the added latency every digital efx-box introduce in the processed chain. There is nothing on the market that offer this, a perfectly latency aligned Clean/dirty bass efx.