Not completely true. I did see certain hands-on videos online and they run pretty well. The latest 10586.63 build is pretty stable for daily use. For the best experience rollback 8.1 or hard reset if on 8.1 >> remove SD card and SIM >> install Windows Insider and update to WM10 >> hard reset >> insert microSD and reset microSD >> start using.
Yeah, sometimes its better to wait until the OS is polished unless you're a noob who prefers the phone must work properly whether they're on preview or stable builds. That's why I refrained to tell OP to use 8.1 until its stable.
I think its better for MS to stop insider builds and continue intensive internal testing to squash known bugs and fix 'em and roll-out to end users. As MS said, w10M is continuously evolving OS and they can introduce new features after few months and eventually restart the insider previews once again. I feel bad, when they continuously release insider builds and in fact there is no conclusion, which features is included and which aren't.