anytime you're reducing your power, or changing your output ratio, you will have some kind of tone change for less or better YMMV.
sometimes, like i said, i like the power tube response of my amp on 10 watts with maximum attenuation....yes, the amp changes and responds differently, but, you dont have to use it so drastically. it's all in how you want to use it, and what tone you're looking for.
for me, it just varies the tonal options already at my disposal and that's what i use it for.
i've tried the power brake and the hotplate. i like the power plug that i linked to...it worked the best, and was the cheapest, which is always a plus.
i bought the 8 ohm one and use it in 8 ohms with my amp with no issues whatsoever.
the only thing you can do is try the one you want, and then resell it if you dont like it...the retain resale value from what i gather.