I had a Chinese tube amp for awhile. I imagine they're all probably made in the same manufacturing facility, or at least with mostly all the same parts, so I will answer your questions as best I can.
Are they reliable? Fairly. Service is going to be an issue unless you know a "guy" or have someone local experienced in servicing tube amps. Most dealers/service centers won't touch them. I've heard some horror stories about grounding problems, etc...right out of the box. Willsenton has gotten some pretty good reviews, so maybe their quality control is better than some of the lesser known brands that are sold domestically in China.
Do they get hot? Yes.
Any experience shipping problems from China to US? It can take a long time, especially in today's political climate and due to backlogs at US ports. I would plan on 4 to 6 weeks, possibly longer. Not kidding. I ordered a pair of speakers from China a couple of years ago and it took 3 weeks to get them. That was a couple of years ago....
Do the export versions actually have upgraded parts?? Not that I am aware of. I know that most Chinese tube amps are used as "modding platforms" and people change out the caps, etc...with higher grade components. The stock tubes on Chinese amps are notoriously crappy, so maybe they're putting in a set of Tung Sol or something and calling that the "upgrade".
I think with most anything you order out of China, it's a crap-shoot. You might get a good one, you might get a bad one. The QC is notoriously poor. Is it worth it? Up to you. There are a lot of Facebook groups the deal specifically with Chinese brands (Yaqin comes to mind). They have all kinds of schematics, modding ideas and instructions, etc...so if you do go the Willsenton route, I would certainly look into that.
Good luck.
