Tuvis was good because of the moral and ethical dilemma. Threshold was just bad on pretty much every level. You could have tightened up the science and it still would have been bad. But, how much can you actually fix the science of a ship travelling faster than light? There's highly theoretical ideas about how it might possibly work but we're nowhere near being able to run any sort of meaningful experiment to test even the smallest part of it. So, you make it fit with the Treknology that's come before and don't worry about it. Then you ignore the salamanders and read a good book.
Watching the Clock wasn't my cup of tea. I bought it on the strength of Christopher's name and previous works that I've enjoyed. I won't be picking up the sequel but that's OK. Not everything has to appeal to everyone. Even now there's some episodes of all four series that I'll watch from time to time but there's also some that I don't bother with.
That doesn't mean I won't check out another non time travel novel of Christopher's. I enjoy his writing, just not the subject of time travel.