I think the cardboard bird-blind is a brilliant idea - simple and inexpensive, and interesting to camouflage.
I watch those birds who pass through my tiny (16 x 20ish) weed-filled 'garden'. The seed-eaters like the weeds, the bug-eaters like the bugs who presumably hide under the weeds. And it's all organic.
I'd like to suggest to people who may want bird-feeders, but are worried about the mess, or who aren't allowed to have one because of the mess - get a bird-bath or similar. If the thought of a cement monolith in the middle of the garden is putting you off, I have a little (3x3) plastic pond-with-bubbler and a platform, presumably to hold some decorative feature. The available water is about 3 inches deep, the water isn't stagnant, and I've got decorative flat rocks around the edges for the birds to sit on.
And its a magnet, all year round.
All the year there are sparrows and chickadees drinking, nuthatches, finches, and robins in the summer, and the occasional crow or flicker, or Stellar's jay, although the last three are infrequent - I think the garden is just small enough that they start to suspect a trap.
The sparrow and chickadees are also eager bathers. There are times in the warmth of summer when there appears to be a line of sparrows, each waiting for the previous bird to finish up having his splash in the pool. Flap the water around, check the underfeathers for completeness, then hop up to the fence to decide where to go next.
And any mess they make dries up, all tidy for the next day.