I have a MEC Sizemaster. I understand the diff between the SZM and the 600 is the collet resizer on the MEC; some have the 600 and a separate MEC Super Sizer. Either would be a better tool for reloading than the Lee. When using the SZM by itself, I can do 4 to 6 boxes an hour. Re Lee. This might be ok if you are only doing a "few" boxes a year. Its not very adjustable, e.g., the crimp station uses "feel" rather than settings. I don't think it has a resizer.
One possibility is to have the Supersizer, load the shot and powder with the Lee, crimp with GAEP tools. Overall this would be less expensive than a new Sizemaster, but you can get a used Sizemaster on Ebay for ~200. A few people who post on SGW do this.
At the moment I am using my Sizemaster to size/reprime, prime, load powder and shot. I do crimping with some of the GAEP tools, I am able to use them to get a better crimp than I can on the Szm. It takes more time to do this (like 3 boxes an hour), but the result for me are factory-looking-crimps with a variety of hulls.
Search SGW for the Lee. Sounds like a lot of dis-satisfaction with it.