I missed the previous discussion, and I have not tried to build one yet. However, I think it makes sense and could be useful for several applications.
For example, I would like to try something like this on my outboard reverb tank, since it picks up hum and radio signals when my band has performed in radio stations or near a powerful station.
I understand the design as an AM antenna coil (out of phase with the pickup coils) terminating to a resistance and/or capacitance pad. The pickup grounds are terminated to the same pad. Probably, the resistance is very small, like 10-20 ohms. The Suhr has adjustable pots to fine-tune the 'noise-canceling'. I would think these could be in series with the pickup and/or antenna grounds. Again, probably a low resistance.
The information I have read indicates you would NOT use RWRP setups with this approach. So, I would have to make some changes on my stock Fender pickup configurations.
The antenna coil may be difficult to make neatly and unobstrusive. It seems like I could experiment though with an old AM antenna from a transistor radio with a single pickup.