I picked up a couple of these TS-3300 boards. They are probably not too interesting as a generic retro PC on their own, but might be interesting for embedded controller projects.
According to the manufacturer, these TS-3300 boards come out of factory with either DOS or Linux in ROM/Flash (can't remember exactly), and the ROM/Flash chip is soldered to its socket.
The problem with this eBay auction is that we don't get to know if the boards come with DOS or with Linux.
I suspect they come with DOS as it's the most common OS, and you could always use that DOS to boot a Linux from an add-on Compact Flash card... but still the eBay listing for this auction is quite poor in details.
Also, the RAM is not user-upgradable, as is comes soldered to the motherboard, and the boards from this auction only come with 8 MB of RAM, which is too little to build a comfortable text-based user-oriented Linux system (in my opinion).