One question would be if you already know how to reload. The 550 is not much different than learning on a single stage. One reason would be that you could run a single cartridge through, while the 650 would spill primers, but this new 750 thingy looks like you could do that also. The indexing would make a double charge a little harder, but that should not be relied on.
As far as price, consider the 650 without the case feed. It will be a little funky to drop a case each time (I would not use the whole tube) but not much different than the 550, IMO.
But if you have a bunch of cartridges to setup the 550 will be a bit cheaper.
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