No, it's really not. Sorry - I know I'll be blasted for saying this but the tuner really isn't one of the strong suits.
I don't have an AX8, so I can't comment on that specific tuner implementation. I do have an AxeFX II XL, and I have performed an A/B comparison with its built-in tuner against (1) a Peterson strobe tuner (mechanical) (2) Peterson strobostomp and a (3) Turbo Tuner.. In answer to the question "why so many tuners?", I have access to a pretty nicely equipped studio, and I also have had a few (ahem) stompboxes on my pedalboards previously.
I found the Peterson strobostomp and the Turbo Tuner to both be amazingly fast and accurate. Those were great tuners for my rigs, and great for tuning guitar, bass and Warr guitar (an instrument with nearly the range of a piano). The AxeFX appears to be on par with those specialized tuners for response time and accuracy. I tested the tuners using my instruments, and also with a sine wave generator. The instrument's signal is obviously more complex, and much less pure, but it's more of a real-world application for me. The reason I used the sine wave generator was to determine the smallest variance in fundamental frequency that could be detected by the tuners. My informal results indicated the strobostomp and Turbo Tuner could both detect when the pitch was off by as little .2 cents, and so could the AxeFX. It seemed to me those two pedals may have been a tiny bit faster in pitch detection, but if there indeed was a difference in time, it was a mere fraction of a second, which isn't meaningful to me in terms "how fast can I tune my instrument". Also, I'd argue that my guitars are rarely closer than .2 cents to being in tune anyway, owing not only to the inherent errors in equal temperament tuning, but because they're imperfect... the frets are expertly crowned, but they're still a curved surface, the same is true for the bridge saddles, my guitars have trem bridges (a complex set of interactive physics in itself) and merely touching the strings localizes some body heat that changes the tuning of that string, which rebalances the floating trem, etc.
If I recall correctly, Cliff posted some time ago that while the tuner implementation in the AxeFX is very fast and accurate, in the communication protocol between AxeFX and MFC-101, the tuner messaging is a low-priority thread. That doesn't mean it takes forever, but that it might not feel as responsive as the AxeFX display will be. As I said above, I don't know how the tuner is implemented in the AX8, so I could be talking out of turn.
I can understand the desire for an always-on tuner on the pedalboard. I happen to like the simplicity of running a single XLR cable from AxeFX -> MFC-101. The only items on my board are the MFC-101, three continuous controllers, and a double footswitch. If I added a dedicated tuner to my board, I'd need to run an audio signal from the rack (where my wireless receiver is located), and also would need to power the pedalboard tuner somehow. For my needs, the built-in tuner does a great job. The greatest challenges for me in terms of staying in tune are more related to the ambient temperature of our stages.