Dear Sarcher, If the CU180 weighs 4 lbs, I personally would to use it on a Mk2, as the stock mat weighs only about one lb. The whole platter weighs ca 8 lbs, I think. So by using the CU180, you increase the inertial mass by nearly 50%. But this is all theory, and if it sounds great, just ignore me.
Since the Kenwood L07D stainless steel mat weighs 5 lbs, you can bet that it flattens out the TI Shield "real good", to quote Big Jim McBob from SCTV. Flat as a pancake; you cannot even see it's there, because I cut it to be very slightly smaller in diameter than the ss mat. I hadn't thought about that issue you bring up in relation to using it with a lightweight mat. Further, the TI Shield has to be grounded in order to work as a shield; I am not sure it would be grounded if used under a non-conductive mat, like the Boston Audio products. Maybe so if the platter itself is bare metal, i.e., not painted or coated with something that insulates.
Albert is lately using the Boston Audio Mat2, on his Mk3. As mentioned above, I use the Mat2 as well on my own Mk3. We arrived at the same place coincidentally. I like the Mat2 a tad better than the SAEC SS300. By the same token, I would be reluctant to use the Kenwood mat on my MK3, because it weighs 5X the OEM rubber mat.
I got this notion about not violating the inertial mass of the stock design from, of course, something I read on the web. I have always meant to check it out with Bill Thalmann, who has worked on both my Mk2 and Mk3, but it does make sense.