Auralex Acoustics Lenrd Bass Traps Charcoal 4

I got a pack of 4 placed in my studio and I'm pretty happy with the result overall, however I've got a bunch of other (partially self-made) absorbers placed in the room, so it's hard to tell how much of a difference they make. I'd suggest buying one pack and try them yourself before you buy a second pack, due to the high price.
They were a bit smelly when I got them, so they spent about 3 months in another room - didn't have the studio by that time yet, so I could afford the wait - now I don't smell anything on them anymore.
If you know what you're doing and where to place them, they might be a good addition to the overall audio quality in your room.

One last thing, don't waste your money on double-sided glue tape, I spent about 30 bucks just to get one hanging on the ceiling/wall corner, which as you guess wasn't worth it. There's glue available here at Thomann.de, I haven't tried that one yet since I got another from a friend, but I think glue should be much easier/cheaper for fitting them on the walls.