@will62, yes I have first hand purchase trial experience of both SS and tube amps in the sub $500 price range through Amazon.com, here's some personal thoughts I can share with you. Keeping it simple, avoiding technical jargon
1) Do these amps sound good?
They sound 'acceptable' for sub $500 range. Unless you venture into 'used' gear, I don't believe you'll ever find 'good' or higher quality new amplifier sub $500 based on a global audiophile scale.
2) How good do they sound?
In general tube amp in this price range will sound a lot better than SS in this price range because tube amp generate current differently so in general can handle low ohm speaker better. However, below are the caveats I found
2a) Gemtune when compared to Yaqin had really poor craftsmanship
2b) Modern Chinese tubes they use in these amp are built to sound like SS. So if you want the tube sound you'll need to roll tubes which will add to cost. Something to think about. Otherwise, out of the box you'll be disappointed that these tubes don't have the signature warm lush tube sound, they sound much closer to a Class D / Class H amp.
3) Most of these tube amps are built from kits, that's why many of them look just like each other. You can cross reference on eBay. Despite my personal bad experience, many people like Gemtune. Like some others here, I would stick with Yaqin as I have read online article that they build their amps out of a modernized ISO certified factory, you should Google about them.
4) Electricals are ok, I wouldn't worry. There are 1.4 billion people in China. In the city of Shenzhen where majority of electronics are made, city is so modernized it makes our Silicon Valley look like 3rd world country, it hasn't burned down yet despite the 12 million population there using so call 'cheap' Chinese electronics. I do wonder how many people here in America plug in their eBay purchase without ever checking the 110v VS 220v setting first.
5) The bad part. I've also previously had Yamaha A-U671 and Yamaha A-S801, both great integrated SS amps for their price. Price aside, compared to these modern Japanese ss amps, these sub $500 tube amps will loss a lot of the detail resolutions. So if you do simple vocal or jazz you'll be ok. But if you listen to large orchestral and enjoy picking out distinct instrument sounds, then you'll definitely have to up your budget.
In the end you'll get what your money's worth, just matter of whether good enough. But I guess that's what the 30day return policy is for.