I have had 1100s for 46 years and highly recommend them, and 870s for 35 years and think pretty highly of them two. I have never had a reliability problem with either gun. I have tried/shot just about everything else that has come along before or since and haven't felt the need to change yet.
The conventional way you load either is first shell in the open port, close action, however many more you want in the bottom loading port.
An 1100, being gas operated, is among the softest shooting guns that exist. This matters to a lot of people shooting hundreds of rounds at clay pigeons. The 870 was once very common on the traplines of America, but the over and unders became the fashionable darlings of gun writers in the 1960s. One advantage of an 870 is that is does not throw empties and possibly hit the guy on your right on the trap field. 1100 Trap models have a small piece on the barrel to deflect the empties down, and they sell shell catchers for the regular models, too.
I love to take my 1100 Magnum duck gun to one particular club. It does not eject the light trap load empties automatically, and this one local "expert" always has to say something, and I always reply "I know, I like it that way." The fact that I am at best an occassional casual trap guy and can usually keep up with him is frosting on the cake.
If you can shoot, an 1100 or an 870 will keep up with anything else out there, regardless of price.