Who makes them? Not teng or it's parent company. They are rebrander like HF. They get the tools to speck via Taiwan and china. The quality of the line is... well bad. At the premium they are asking, they should have updated the line long ago. The whole schtick is modular foam/plastic trays for they boxes.
I've used a few of the tools when I was in the UK, most where not up to par with what Taiwan has to offer today. Funny enough, most of them where on discount. No one ever bought them, they brought sealey or laser instead.
I think quite a lot of us Brits ended up with some Teng because some magazines used to give away small 3/8" socket sets with an annual subscription (which is how I got my set, sockets OK, ratchet awful, but even cheap sockets are good nowadays) which is actually not terrible compared to some of the junk magazines used to give away.
Teng was also pretty commonly found in independent retailers, think motor factors and small tool shops, they would have displays with a lot of open stock single items available and individual modules of their storage system, expensive for what it is but I bet a lot was sold to people half way through fixing their car and they discovered they needed a tool to get done, and Teng was what they could get at short notice.
Their tools should be better than what they are for the prices they charge, nowadays with the Internet it's easy to buy anything you want, so what local shops stock has much less revelance to what people choose to buy.