I've not tried paddocks yet but plan to this year. The main threat I see with paddocks is from hawks, but with the Chickshaw inside the paddock, the chickens can run underneath if a hawk appears.
Regarding the seed mixes, if you can afford to plant more than the suggested amounts you'll have better success, in my
experience. I wish the seeds weren't so painfully expensive! Make sure you seed
after a patch of ground has been cleared by the chickens, because the natives start much more successfully on bare soil. And yes, I'd go with a 50/50 combination of those two mixes. If I get my paddocks up and running by Fall (the best planting time) maybe I'll try seeding those mixes myself. Up to now we've mostly planted wildflowers (success!) and some grasses (not so much success). The secret seems to be to have a nice bare patch of dirt, a lot of seeds, make sure they are raked and pressed into the soil surface, and plant in Fall. And if possible protect from deer (and sheep, in my case).