I have two sets of Ruby tubes in different amps, great tubes. Absolutely nothing wrong with them.
As mentioned they are a rebrander, so they get their tubes from the big three. Which one is not relevant really, as Ruby matches or rates the tubes they get. The tube you get will be tested to be of known quality.
And for that matter, even China-made tubes are GREAT. Hate to say it, but they make good tubes in comparison to the other two major factories. Where I think the difference comes in is QC. JJ and the EH New Sensor factory have a higher level of QC and have fewer duds in the marketplace. When someone says they don't like X tube, there is almost a 33% chance it came from one of three factors. If someone says they hate JJ then they prefer Shaguang tubes and EH-made tubes over JJ. Etc. etc.
That said, Ruby tubes are great tubes, because they are tubes that work.