I have both devices.
The ColorMunki Photo does not play well with papers with OBA's. The i1 PhotoPro 2 uses another light (LED) on the second pass over the calibration charts to analyze the OBA, and the software can generate another chart (5th sheet) where you view it under the lights intended and eyeball in the 4 patches that run from a slight bluish tint to a yellowish one. That helps with the OBA in the glossy white papers and canvases.
The i1 takes 4 sheets of paper to produce an ICM profile and the default is around 2033 color chips. The ColorMunki Photo takes 2 sheets and far less color chips (I can work the driver to print out half the chart on page, read it, and print the second chart on the opposite end so I can use one sheet now.). The Color Munki is faster overall, but it can cause read issues with some white or metallic papers. Usually the shadows will get blocked up with my Munki and shows as a sharp light to dark transition in a graduated grey scale around a RGB value of 40,40,40 or so. The i1 is often smoother there.
As far as monitor calibration, the i1 can take up to 24 minutes to do a run through in the Max. analyze mode. The Munki less time, maybe 5-6 minutes as I recall. The i1 will also read 9 areas of your screen in advanced mode and tell you the Kelvin of each area as well as the brightness differences. Can't do much about the Kelvin or area brightnesses as that is factory set, mostly just to show how good or bad your monitor is.
Really depends on the papers you use. OBA papers will probably be better suited with the i1. Matte and non-OBA and the Munki might suffice.