The Ethos has more shell capacity 4+1 and the Monti is 2+1. I personally like the two piece receiver, it does come in handy for cleaning and I haven’t seen any negatives to it.
I have an Ethos and a 828U which I shoot equally well, and I carry the Ethos for the light weight with extra firepower.
You can put a new carbon fiber high rib on the Ethos, and I like it that way.
Factory tires are crap. I bought a slightly used f150 a few years back and it had what you described. Took it in to get the tires balanced, and it ended up that the tires were out of round. Put on new tires and it was gone.