I have been using the 21 st century neck turning lathe for over a year now, and it works great, everything John makes is top quality.
Compared to the hand held K&M option while holding a drill it is far superior, and gives no fatigue to your hands, can turn cases all day long.
You do of course have to use some cutting oil/lube and take a break to make sure the cutter does not get heated, as it will warp slightly, do a few cases and give it a minute to cool, goes for all neck turners really if you want consistency.
It is also faster and easier to use, and for me at least provides more consistent results then holding the turning tool by hand to give it some self alignment.
The cutters designed specifically for each type of case shoulder, to make the proper relief cut makes the inside reamer almost useless from my experience.
The case holder design is also very nice and does not scratch or mar cases at all.
Available spare parts for everything, witch it important for someone like me that lives far off, if i loose a set screw i can not call and have a new in the mail next day.
And of course a lifetime warranty for the product, also excellent customer service in my experience.
A mini lathe with a K&M or 21 st or PMA turner is a better option though but expensive.
You will need a expander die, expander mandrels and turning arbors, witchever producer you choose.
You must also stick to one producer for most of these.
21st century shooting, sells arbor adaptors for K&M mandrels, so you can use they're inside reamer if needed. Or one already has they're mandrels.
Mandrels and arbors are interchangeable between 21 st, Sinclair and PMA so you have the option of witch one you want to use.
K&M does not fit the rest.
If i was to do it all over again what i would buy is:
21 st century neck turning lathe, with the appropriate case holders and cutters for your calibers.
21 st centruy Lathe Accessory Package
21 st and K&M arbor adapter.
21 st century expander die.
PMA tool carbide expander mandrels.
PMA carbide turning arbors/mandrels.
K&M expander , and tuning arbor with cutter if unlucky enough to get doughnuts.
PMA tool neck turning oil.
If you ever need to neck up cases like 6,5-284 to 284, a PMA Tool carbide neck up mandrel.
What i have of mandrels/arbors are 21 st century Tin Coated SS steel, works good, but Carbide is better if your willing to pay the price.
Another option for neck turning, that i have no experience with, but have heard good things about is the Gracey powered neck shaver.
Someone can probably chime in on this.
ANd you will need a good ball mic, K&M offers a service to modify them to fit better for measuring neck wall thickness witch is excellent.
German Salazar did a short review of the neck turner at riflemansblog (his site) if you are curious.
21st Century neck turning Lathe and concentric results - YouTube
21stcenturyshooting.com Neck Turning Lathe - set up and use - YouTube
The last video is very detailed but sleep provoking.
Everyone has they're preferences when it comes to reloading tools, this is just what works best for me and what i would buy.
The K&M turners can give excellent results too, just harder to achieve from my experience, as it is hand held.
The PMA turner i have not tried, but heard good things about it.
And you have gotten some excellent advice already, good luck with your neck turning endeavor.
it's a stock