The answer is no, it's not as good as it seems. The size is good, the interface is good but the resolution is only so so.
it's not good enough for checking "critical" focus on the screen, especially outdoors.
Leaf Capture does offer a good live view option when tethered to a computer – nothing close to what a current dslr offers, but it works for non moving objects under good light, indoors, tethered.
The best option for checking critical focus outdoors on an LCD screen is with the IQ series from Phaseone, the new H4D's, the Pentax 645D or the Leica S.
A workaround (if you're shooting from tripod) would be to take a laptop with you when outdoors, pop in the cf card, download the file and check the focus on your laptop.
Otherwise, the Leaf makes beautiful files. Imo, the nicest file of all MFD backs.
If your shooting on a tech camera you can also use a magnifier and the ground glass, just like the film guys always did ; )