No, I’m not noticing any noise with it, nor any compression or other artifacts. It’s about as transparent, beyond it’s intended effects, as anything else I’ve heard in my respective chains.
It’s worth bearing in mind that almost every piece of music you’ll hear/buy/stream today was mixed with the same software EQ tools we’re talking about here … so any un-intended qualitative effects they’re going to have you’re likely already being subjected to (not that adding more wouldn’t be bad).
The results of software/digital EQ are very dependent on how they’re implemented. Some are shockingly bad and very obvious, but most of the serious products (which aren’t necessarily expensive) do what they do with no audible impact otherwise.
True-Fi is, however, not a traditional EQ product … it works with presets for specific headphones rather than allowing arbitrary adjustments. After choosing one of those, you can add some level of bass enhancement as well as compensate for age-related hearing loss, but those are the limits of it from an adjustability perspective.
This makes it much easier to get appropriate results with.
One major benefit you get with software based tools like this is that they’re typically available with a free trial, which makes it very easy to see for yourself if they are doing anything negative in your system.