My thoughts with the clone brands was that while the specific patent for the lego brick is quite up in the air, it always did make me wonder why companies like Disney didn't go after them instead of Lego themselves chasing them for IP theft.
Because even if the Lego brick patent is not protected or has expired, the fact remains that the design of the set itself belongs to lego designers, and the IP in cases like star wars would belong to disney, whereas the clones of Lego IP's like Ninjago and Bionicle are within the lego IP.
So while little could be done about the bricks, it does make me wonder about the IP.
The likes of Oxford is interesting because the sets I have seen of theirs are unique in design, their titanic and effiel tower sets are their own designs rather than being a rejig of an existing or out of production lego set.
In terms of buying them, most of the sets I am interested in are within a realm of price that is too close to lego for me to be bothered buying the clone brands.