We've been running registered and commercial Gelbvieh and Balancer cows for over 15 years, as well as some other breeds including SimAngus, Braunvieh, reg. Angus. The Gelbvieh and Gelbvieh influenced cows have worked the best for us, with overall good disposition, milking ability, fertility, and growth.
However, as is often stated, there is a great deal of variation in all of the major beef breeds. So, it is possible to find calm and flighty Herefords, good marbling and poor marbling Angus, and good milking and poor milking Gelbvieh.
In response to denvermartinfarms comment of poorer milking Gelbvieh cows, this didn't surprise me much. In the late 90's and into the 2000's there have been a handful of popular Gelbvieh AI sires that were used extensively across North America (most of these were "pretty" show oriented type cattle). Unfortunately, as these bulls daughters started coming into production a few years later, many of them didn't milk very well, and so over time the milk EPDs of the sires started going down. In my opinion, it is disappointing that some high profile Gelbvieh producers have continued to use these low milk bulls (and their sons). However, for many of these breeders it is more important to win the purple banner at Denver or Louisville than to produce cattle that will work for their commercial customers.