I downloaded the Studio One demona few days ago (Mac version), really because I thought I'd see what the fuss is about and switch to it if I find it does a better job for me.
Now, bear in mind this is the Mac version and some of my initial impressions may not hold for the Windows version.
The first performance-related thing I noticed is that latency in S1 is worse than I get in either Sonar or Logic at the same buffer/bit depth etc. settings. Not much, but noticable. To get the same latency (actually very slightly less) 64 sample buffers give in Sonar or Logic (which perform equally) I have to drop the buffer to 32 samples. Which does not help cpu usage at all.
I find S1's way of doing many things fairly unintuitive, certainly harder to switch between than Sonar to Logic (or vice versa). I find myself reading the manual for quite basic things I could 'just do' in Sonar/Logic because how to do it was obvious. At least to me.
S1’s plugin management isn't particularly good, it shows the AU, VST and VST3 versions of plugs at the same time without distinguishing between them and duplicates a lot of entries in the list - e.g. Plugin X might be listed three times under the company name 'Plugin Maker' and again under the company 'Plugin Maker Ltd."
I'm not keen on the gui either, though that's a personal preference. Not keen on the meters either.
So far I'm finding it hard work to use and I'm not at all sure I'd want to use it as a main DAW. Having said that for someone new to DAWs it may be more easily understood. But the latency issue is a definite, reproducible downside and I need low latency for DAW-monitoring quite a few tracks at a time.
On the plus side it installed easily enough, it remains to be seen if uninstalling is as simple.
Another plus is that it tells you what the latency each plugin is adding is, which is very useful.