Look over the MEC website before you decide ...
http://www.mecreloaders.com/ProductLine/Product.asp
The 600 Jr isn't a bad machine ....but yes, add the primer feed. You can get about 4 boxes an hour off the machine. Recob's target shop out of Wisconsin sells it new for about $ 135 / and they're a good company to deal with / I've bought lots of loaders and lots of components from them.
http://www.recobstargetshop.com/browse.cfm/2,197.html
The sizemaster, in my view, is really there because you can adjust it for 2 3/4" or 3" shells ...so its more designed for the "hunter" vs a target shooter. It doesn't increase your speed much - its still a 4 box per hour machine in my mind.
The next step up - is the Grabber / and its the first in the line of the progressive machines and will give you about 8 boxes an hour / so it really increses your volume. Recobs target shop sells it new for about $ 370.
9000 GN is a better machine than the Grabber / and its $ 60 more ....but it auto indexes ..so its faster easily 12 - 15 boxes an hour.
9000 HN is their hydraulic ( which I like / but you need a permanent location for the motor and pump that rests on the floor ) so its not portable. Its a little faster than the 9000 GN - ( call it 15 - 18 boxes an hour )...
On the easy pak ...sure they work / but I'm lazy ....I toss 30 shells into a quart sized zip lock bag ( gives me a few extra shells per round) ...and then put 10 bags into an 8 gallon tupperware tub...
Going with a Jr isn't bad / and they're easy to sell ...but time is a factor .. / so I'd take a serious look at the Grabber model instead. ( I know none of this stuff is cheap / but you'll have it a long time ...)...