Summing stereo music to mono causes changes that might be unwanted for you, depending on the type of music you listen to. Stereo is better sound if you can arrange for it.

Best solution is to put stereo speaker sets in each common listening location. Your example of hearing something different at the sink than at the table is merely a question of distance and speaker placement. Sound spreads out a lot, so it might sound fine in both spots even though the stereo imaging won’t be standard.

Music hopefully is produced to minimize mono-summing problems, but some issues are hard to fix in mixing and mastering, and they can’t fix everything perfectly. Phase problems caused by mono summing can cause some instruments and voices to become louder or softer in the mix than the original artist intended.

I have no idea how things like those crappy little voice activated speaker pucks handle it. Perhaps they try to aim two speakers outward from each other to get some tiny amount of stereo separation. Possibly even with a bit of deliberate L/R phase nudging to prevent mono summing problems. Dunno.