I've had 3 I-40 cameras. Eventually all 3 digital displays went out. They were all out in less than 1 year. Cams were still useable since I knew the setup. I loaded them with batteries, but relied mainly on external power. Two of the cams quit working on batteries only. That appeared to be from water getting into the battery compartments and causing corrsion. Daytime pics were great. Night pics were great if the animal was still. If there was any movement the pics were blurry. I would not recommend the I-series cams. One of them has now been stolen...no big loss (or gain for the thief). One no longer works at all.
I've had great results from the D40s. I have 3. Day and night pics are good. One of the cams did "freeze" up in extemely cold weather. A couple of hours in the house and it came back to life. I would recommend the D40s based on MY experience. I just go two new bushnells in the mail....up until a few months ago I saw nothing but great reviews of bushnells...the 2010s seem to be shaky.
My rule of thumb: All trail cams are junk and get bad reviews...just pray for a good one.