i've got the Weber too, does a perfectly good job, and considerably more affordable than the competition. like the others, with extreme attenuation the tone deteriorates, but i think that's largely because the speaker isn't working so hard anymore.
as with most guitar related things, there's a lot of snake oil and bullsheet involved when these come up. as far as i can tell, all the attenuator's do a similar job. whether or not you like the end result of one or another is mostly down to personal taste. just like with the amp's they're plugged in to :)