I also had a 2018 6 Signature, first one available in my area. I used it for commuting (1200 kms/week) and was always impressed with the stellar fuel mileage on the highway ( I averaged 7.4L/100 kms) and how much of a cruiser it was. I was very sad the day I traded it even though it gave me a lot of trouble.
I did have a different experience which was somewhat of an anomaly, however. You can check out all my threads. I ended up ditching the car last year because the engine had an issue that warranted a full engine replacement and there were constant issues that drove me insane.
I don't find the car faired well in snowy conditions on the highway, either. I am not sure where you live and if you will have to drive the car in slushy conditions. The under panels foldded and dragged on the road due to ice/snow accumulation and me and the dealer ended up removing almost all of them because the ones that were left vibrated against the bottom of the car and it was beyond annoying.
I didn't find the engine was one that liked to play either, I equate that to the 2.5 turbo being originally used in their SUVs (I have a CX5 now, which is a great match for the engine). I loved the low torque and that the engine never really had to work hard to pull hard. It wasn't an engine that I liked to rev out.
When you're checking out these cars, make sure you monitor for rough idle when sitting in traffic and check for misfire codes even if there is no CEL. Mine (and others with 2.5 turbos in other vehicles) had this and it was due to a manufacturing defect with valves not sealing properly which meant they needed to replace the engine. I had the 2nd 2.5 turbo that my dealer had to replace the engine in and was speaking with a member on the west coast that had his CX5's 2.5 turbo replaced as well. After the engine was replaced there were numerous issues (fuel leaks, PCM failure, incompetent people working on it leaving things unfinished and damaging more). I would stay away from a 6 that has had the engine replaced as they reuse too many one-time-use gaskets and it's just asking for trouble out of warranty....or in-warranty as was the case for me.
Also, watch for broken plastic trim on the seat backs. These are the metal-looking trim bars that are in the leather where your back hits the seat. It's cheap plastic that isn't fully reinforced and snaps off at the end and it's a royal pain to replace them. Horrid design. All you have to do is put a little force on them and the ends snap off from the leather shearing the end off the trim.
Again, my experiences were not necessarily typical but it wasn't unique either.
I am now in a 2020 CX5 Signature and it's been pretty good thus far (8 months in).🤞
Best of luck in your search!