I had a ZTTO stem on my road bike for a while, no issues with it. It was cheap and reasonably light. I have no experience with their shorter mountain bike stems though.
I'd be a bit wary of the "Redshift" one since they are blatantly ripping off Redshift's name and logo. Redshift doesn't list any rigid stems on their website (redshiftsports.com). This doesn't mean that the stem is bad, of course, but it doesn't give me any confidence.