Originally Posted by Sardines

I am only familiar with the C.62 SLT version, which is the carbon version of the SL Road. The geometry is probably a little different so I'll just cover the nuances of the Cube design as I know them.
First of all, it's my neighbor's bike but he did a lot of the mods in my workshop, and I've ridden it over a couple of weeks myself. The biggest flaw of the GRX is that silly switch to turn on the clutch. SRAM's roller bearing clutch system is always on. He switched out the Shimano RD to the SRAM GX 2X11 long cage RD, which also allows 10-42t cassette, which gives the 46/30t crank a lot more top and bottom end, even if the gears are wider apart. There is some cross chaining but that's what the FD is for.
The fenders from Cube (ACID, if I remember correctly), are plastic and the rack is installed into the fender and acts as fender support as well. They were well made but the fender is short and spray kicks up a bit. So we switched out that Cube system for the AXIOM Streamliner 29er and the SKS Edge AL 46, which added 300+g in weight but the AXIOM mount is about 4cm back from the axle and also braces on the fender bridge. The annoying thing is that the fender/rack mounts face internally, so any maintenance requires rear wheel removal, where the GX cage lock is so much easier to deal with.
The other upgrade done was the brake levers. The Tektro levers don't have stroke adjustment and were pretty long stroked, So switch to the Shimano XT levers gave better stroke adjustment. Otherwise the HD280 pistons are good enough for a bikepacker/commuter.
Overall, the Cube looks and feels well made, and seriously that single rail rack is simplistic, and great for a commuter. However, if you want to add trunkbags etc, their bigger racks are just a little too short for certain bags.