EQ Acoustics Project Corner Traps grey

Carefully placing a few of these on both my recording and control rooms definitely made a difference. 90-degree corners are a huge acoustic problem and these will help a lot improving room acoustics on all frequencies.

Pros:
Cheap and effective acoustic material.
Lightweight
Easy to apply

Cons:
They don't look as smooth as the pics suggest

If you're on a budget like me these are an excellent choice

very thick and sturdy.
does the job very well, you might need to think about how to glue them to wall as they are heavy, the strips won't work as they came off the wall in a few weeks.
what helped me was adhesive spray.
highly recommend

After adding sub to my HS8's I needed to tame lows.

Adding 8 of these and tuning the room with SonarWorks has changed my life

I was a bit tight for space in a corner because of a door, but these fit that space perfectly and offer good absorption.

Don't attempt to mix anything on monitors (with sub or not) without setting up, treating and tuning your room correctly.

most effective bass trap for lowest price

I have a bunch of these in my studio - Easy to install and look cool!

Fantastic noise absorption highly recommended.