I have owned both tools, using the Evo all last season, and the RT this season -- with 2 kids racing, I've sharpened many pairs of skis with each machine at this point. I really think both tools are great, and have been a huge win in allowing me to quickly achieve predictable results. I'd say that both are capable of achieving great sharpness, so the choice comes down to usability. Neither tool is perfect, and the tools have very different usability issues to manage.
The biggest flaw of the Evo is the extra sidewall clearance it requires, compared to the RT. With some skis, I had to remove the brakes before sharpening; otherwise the machine contacts the brake, resulting in a short section under the heel where the edge gets flattened rather than sharpened. This absolutely isn't a problem with race skis, or really any binding setup with a plate or any significant stack-height. I did have this problem with my kids' rec skis (mounted with Marker 4.5 bindings), and with my all-mountain skis, flat-mounted with Tyrolia AAAtack 13 bindings.
The RT is bigger, heavier, and requires a more stable platform. I use a portable Swix waxing table for all my ski tuning, and because of the side-pressure needed to compress the spring-loading, the table tends to tip over. This can lead to inconsistent results
. I've temporarily 'solved' the problem with some bungie cords and an old wooden pallet.
Both machines require you to carefully manage the power cord. If you get it snagged on a vice, the end of the table, a ski brake etc, you'll end-up messing up an edge. The Evo is a ~little~ more fussy than the RT here, but it's essentially the same issue with both machines.
A final major point I'd make is that mistakes with the Evo tend to be higher impact than with the RT. Just about any slip-up with the Evo results in the aforementioned edge flattening, which takes quite a few additional passes to fix. The RT is a little less likely to slip-up, and mistakes are in general less damaging.
Regarding disc wear, I don't have any concerns with either the Evo or the RT. I haven't observed any disc wear at all with either machine. If anybody is using these machines commercially, maybe they could comment? I expect many seasons before having to think about a disc replacement.