I found the opposite to 'Heystack'. My Rothwells (-10db and about £40) were a solid purchase. I did notice more detail, an initial overblown presentation that calmed over the first few days, but finished at slightly warmer than before (a happy by-product for me).
If you've ever spent ages stabbing your remote control to achieve a small increase in volume, only for it to shoot up just that little too much, attenuators allow a greater degree of control.
Just be aware, we're talking subtle changes which you may or may not deem to be improvements. Don't expect to radically alter your sound.