honestly, after owning several THD, Alex, Weber, TN, etc..., I would just save up for one of the modern units. I've gone through a lot of the passive ones, and they all seem to take something away, at least to some degree. If you're like me, you'll dig it for a bit, then plug straight in one day, and throw it in the closet.
I currently have a PS100, and it's been the most transparent feeling and sounding attenuator I've used. I haven't tried an OX, but they seem highly regarded as well. The one downside to the Fryette stuff is having tubes, but I guess it's a plus as well if that's what keeps it feeling "alive". Also consider the horror stories over the years you can read with people using the older units and blowing OT's. I think the newer stuff is much more friendly with transformers, at least from the feedback I've read. It's worth it to spend a bit more with an attenuator IMO, since it's tied to your amp's health. I justified getting one by considering it can work with any amp I own, and having an FX loop after the power amp is very useful.