I hate to be that guy who listens to all the good advice then goes against it, but... I have a DK4210SE and have had a CK4010se as well as a Kubota B2610. All reccomend caution about shifting on the fly, and as I tested it out at slow speed with no torque on the machines, they all have shifted smoothly without incident for years. I still do it and have never had the tractor misbehave when I do it (literally thousands of times now) and it shifts at any speed smoothly, not telling you to do it or others are wrong, just adding to the great advice you already have. Cheers