I used one for about 18 months and experienced very inconsistent results due to clumping and inconsistent doses. This resulted in extremely uneven extractions and the need to updose sometimes up to 24g for a double shot in order to even out the inconsistency. I don't have any experience with any other doserless grinders, but I would take a Robur any day.
Hope that helps, I like Simonelli as a company and their techs and customer service reps were always extremely helpful, I just couldn't get consistently great results with the Mythos.
I've heard of similar problems with the La Marzocco Swift grinder. I've never worked with either of them, but the I find the Mythos more appealing since it can hold an entire 5# bullet of espresso beans (I'm all for convenience). You can also order models from Nuova that either come with or without the built-in tamping mechanism, which is nice since Marzocco's Swift only comes with the spring-loaded tamper. Mahlkonig has it's cool doser grinder, but I don't know a thing about it.
If you're going for highest controllable quality, stay with manual grinders. Since you said you're looking to switch to the doser systems, I'd recommend the Mythos. The few times I've played with it, I haven't had a problem.
The one I am looking at is the low rpm temp stabilizer. Is that the one you had problems with?
It is. The grinder was fast and cool (temp. wise), but far from consistent. My experience with the Mythos made me want to use dosers from now on. The low RPM kept the coffee cool, but the dose and clumping were too big of a problem consistently. I have talked to several people that have really like the COmpak K-10 doserless, but I don't have any experience personally with them.