I've owned a Tern Link Uno for the last 2 and a bit years. Its a fantastic bike, I commute everyday on it and it's our go to bike for a quick nip to the shops and so forth. It's been ultra reliable no matter the weather and gets ridden in all conditions. The D8 is essentially the 8 speed version of my bike and is generally a really nice bike.
The ride itself is really nice and surprisingly was noticeably stiffer than the Dahon I owned previously. The fold is easy to do and quick once you get used to it. Obviously not as small as a Brompton, but plenty small enough to fit into the boot of a VW Polo if you need it to!. I regularly carry mine up and down the stairs to the train platforms with no problems, it's quite easy to carry unfolded. The magnets that are supplied, are bugger all use at keeping it together when folded though.
The finish of the bike has stood up really well to the last couple of years abuse as well and there are very few chips and marks on the frame. Standard kit supplied is a mix of high quality, like SKS guards and no name components like the chainset. Be aware that the Drivetrain is very close to the ground because of the small wheels and would benefit from a regular TLC to keep everything running sweet and prevent any issues or problems.
One big warning with a secondhand Tern is to check it's not one of the frames caught up in the recall a few years back. Both Links and Verge's manufactured in one factory, suffered from broken frames. After I purchased mine, I checked the frame number and found that it was within the range that was possibly part of the recall. I contacted Tern and they replied in days to reassure me that mine was not affected. I was happy to believe them at the time and two years and thousands of miles later there's been no issues.
Another issue is the weight limit. I am a relatively light, at about 65 kg. I have a colleague at work who is tall and stocky and weighs about 90 kilos. Fully dressed and carrying his work bag he exceeds the weight limit for his Tern Link D8. Just recently he's been having problems with the hinge pin and needed it replacing. We can't say for certainty that this was a weight issue, but it's worth keeping in mind.