If the Lee Collet is not available then you can send a fired case to Lee and they will make you one. The Lee Collet is simple to use and does do a fantastic job of reducing runout. It would be worth the wait.
However, if you want to try the Redding Bushing Dies, then I would recommend that you also have 2 other pieces of equipment. The first would be necessary in order to have a good way to measure the neck thickness. A ball micrometer and a stand
and the second would be a way to outside turn necks. I use the Forster hand held turner but there are others
The thing is that a bushing die will size the outside of the neck to the size of whatever bushing you buy. That will push all the variances in neck thickness to the inside of the neck. You could leave the expander ball stem in but you might as well use a regular full length die if you are going to size your necks with an expander ball (lot cheaper). The bushing type dies are at their best when used with no expander.
So if you are sizing the outside of the neck to a certain dimension and have a neck thickness variation of .002" from .013" to .015" (very common), then that variation will go to the inside of the neck and cause runout and varying bullet grip. Turn the necks for a consistant .013" overall thickness and you don't create runout.
To figure out what bushing size you need then measure your neck thickness and decide on the amount of bullet grip you want. For example if you turn your necks to .013" and want .003" bullet grip then
caliber+neck thickness one side+neck thickness other side-bullet grip=bushing size
Now some contend that the less bullet grip the better when it comes to runout. That is one of the premises of the Lee Collet which will only give .002" bullet grip (the mandrel is .002" smaller than caliber).