I also have the purple tops and planted them this year, they are baseball size now and looking tasty if we get some snow! Broadcasting will work fine before a rain with some initial weed control and some tillage. (for me it did at least) We get a lot of snow during deer season so it works good for the last few weeks.

purple top turnips worked great for me this year. Deer didn't really mind them until Mid January but then they were gone down to the roooot.

I just use the variety at our local co-op. Deer usually eat them until it comes a freeze, because the sugar content increase then.

I plant the evolved harvest rape/brassica blend and as soon as it cools off the deer love em, to my understanding all brassicas produce more sugar during cold spells.