I have GIK corner bass traps. They are very effective in the corners behind my speakers. They didn’t do much in the corners behind my listening position...so I stack two of them in corners behind my speakers.
apparently the bass pressure was greatest in the corners behind my speakers...which makes sense due to closer proximity to speakers than corners behind me.
i would say they are pretty effective down to 60hz...going off memory they start rolling off at 80hz. They have scatter plates attached as i didn’t want to risk having a dead room.
There is also an option to add a range limiter plate, which focuses on absorbing more bass and less mids and highs....which is what you want because due to lengths of wavelengths, there will be a surplus of longer waves (bass) and a shortage of shorter waves (treble).
To answer the question of whether or not bass traps are needed I think it's a function of room size (close reflections vs longer reflections). If you have a 20x30 room bass traps are more of a nice to do but will definitely help. If you have a 12X16 room, bass traps are going to have obvious improvements if you buy the right traps and put them in the right places.