Opinions on poster strips and cheapest place to buy?

[Mew]

I'm an avid poster collector. Up until now, I've always been using reusable tape, regular tape, and double-sided tape to put my posters up (only the reusable tape touches the poster and then I put a piece of double-sided tape on it, then regular tape is what actually sticks it to the wall-- complex, I know). Anyway, I need to redo the posters on my walls (and ceiling). I've heard of Poster Strips by 3M but have never used them. So, questions for those who may have!

1. Do they really work?
2. Do they really leave no residue on the posters and don't cause ripping when removed?
My posters either have a glossy finish or are paper matte-ish.
3. Do they work on ceilings?
My ceiling is the same material as my wall but I'm wondering if the strips can handle gravity.
And would they be easy to remove from the ceiling?
4. Does it only take 4 strips, one at each corner, to hold up a poster?
5. Where's the cheapest place to buy?
I need enough strips for at least 40-45 posters and while looking around, the cheapest I've found is like 200 some strips (multiple packs, of course)for $30.

Any help would be appreciated-- Thanks!