The 5-10 uses the same micrometer-style minor poise as the 10-10 scale. It's just 500gr capacity instead of 1000gr (okay...510 and 1010 grains).
I suspect it was discontinued because of the extra cost to make the micrometer poise beam. There's lots of other 500gr scale choices for less money.
The 505 has two notched minor poise tabs to cover both the 1gr and .1gr increments.
In theory, the micrometer poise is infinitely adjustable even in between .1gr minor adjustments. But the 5-10/10-10 is only guaranteed and calibrated/graduated down to .1gr just like the 505 so there's really is no advantage other than personal preference.
The Dillon Eliminator is identical to the RCBS 505.
Both of them are Ohaus scales and use the same notched triple-poise beam. So which ever one you can get at the best price is the way to go...don't be a color snob.
Like Waldog posted, blue is cheaper than green.
The RCBS 502 and the Lyman Pro500 are similar to the Eliminator and the 505 but only have a double-poise beam and are a bit cheaper yet.
The old (discontinued) Hornady/Pacific beam scale and the Redding beam scale are twins and are the only two major reloading company beam scales besides Lee that aren't Ohaus built. There's nothing wrong with these either.