Update:
I've just checked, and I don't that's correct. I tried both the ColorMunki Display and the i1 Display Pro using the latest Argyll software (v1.7.0) via the latest dispcalGUI (v3.0.2.0), using the same settings for each device, and the the i1 Display Pro is about twice as fast.
I'm afraid it would appear that the ColorMunki display is crippled in speed.
I am curious about what "twice as fast" means. How long to produce the monitor profile with each instrument.
In any case, the OP mentions his concern for instrument
cost. I think he is less concerned about speed.
While I'm about it, let me express my thanks to Graeme Gill and Florian Hoech for their excellent software.
My experience, using the ColorMunki Display and Argyll/dispcalGUI is that it requires nearly 60 min. to produce a profile. No problem; I can have dinner and watch the news while it works. The results are damn good, both in terms of numbers and matching prints to screen.