FWIW, I'm one of the VibraPrime crowd. Had one years ago, worked well enough but eventually it broke, and IIRC they stopped making them for a little while. When I got back into loading on a 550, I ran with the old school flip tray and hunt-n-peck method for a while, but eventually got a new VibraPrime. Tempted to buy another just as a spare, just in case.
Personally, I'm at the point where I'd really *like* to have an RF100, and I may end up getting one 'just because' - what can I say, I like the hands-off automation aspect of it. That said... it takes me maybe five minutes to load up 4-5 tubes using the VibraPrime, and I very, very rarely ever load more than that in a single setting, so I do have a hard time justifying the jump from the $40 tool to the $400+ option.
I'm really surprised, though, that between modern 3D printing, small shop CNC manufacturing and micro-electronics that we haven't seen a few more entries in this category. I mean, it's pretty much a) use a Dillon flip tray, b) VibraPrime ($48-ish), c) Dillon RF100 ($360, plus $53 for the conversion to large or small primers respectively), or d) something like the Camdex, which I think runs a couple grand?. That's a pretty dang steep gradient to the field.