Nothing wrong with the 550B.
I use mine for both pistol and bottleneck rifle, though I found I have to "break out" resizing/remove case lube/trim and then resume with progressive operations, for rifle.
The only modifications I've made to my press are the UniqueTek turbo bearing -
http://www.uniquetek.com/site/696296/product/T1281
and the micrometer powder measure bars -
http://www.uniquetek.com/site/696296/product/T1231
There is nothing wrong with the Dillon design, but these make it better.
Of the two, I really like the smoother indexing operation with the turbo bearing. I understand a similar thrust bearing can be purchased from McMaster-Carr for around $5, if you don't like UniqueTek's price.
With the micrometer powder measure bars, I find I can quickly change to a different load for that caliber (toolhead), but all it does is save a few minutes of trial and error adjustment with the original Dillon bolt. So I'd classify it as a "hassle remover" rather than a real improvement.
The primer tube thing makes for a nice break. Yes, it is tedious, but it is not fragile.
Something that may not be obvious is that there is a corresponding plastic finger thing at the end of the magazine tube, above the primer slide. After a couple of thousand rounds, I managed to wear this out. Easy to replace, and then I was back in business.
It is probably a good idea to get a replacement for this part, in both sizes if you reload both small and large primers.
Something else that can be done is to get spare primer tubes, if you don't find reloading primer tubes to be a relaxing break from the press. Then you can load up 4 or 5 and settle in for reloading 500 rounds with only a brief pause to refill the magazine on the press.
I like my 550B and I wouldn't replace it with a more automated model, even if someone gave me one. I find it is "fast enough".
