Send me the model 12, and i'll give you my 870.
But really, I've had an 870 for 26 years. I shot skeet and trap competetivly with it. Used reloads almost exclusivley, and when I was into the competition would shoot 200-400 rounds per week. The worst problem I had was the bruised shoulder! Ouch. Never had a jam, or misfeed.
I was 14-17 years old during this period, but I won many many matches against folks using Browning superposed, Rem 3200, and Rem 1100s, and all kindss of fancy guns. I was nicknamed Mr. Automatic Pump :)
It is an extremley reliable shotgun. However, I do not know anything about the "express" version of this gun.
As far as cleaning the 870:
1 Take the barrel off
2 Clean with rod/patches, or a bore snake.
3 the slide, and "bolt" mechanism slide forward, by pressing on two levers under the loading area. Clean these, and the inside of the reciever
4 use rem oil on pump tube, and slides, and side of "bolt"
5 re-assemble
When I shot a bunch, I would clean it every week, but now, I'm not as hyper about it.