Anyone ever use one or know how well they work? Can't seem to find much info on them anywhere.

Offenhauser made some Tunnle rams that had dividers in them....It was pretty darn rare to see anyone useing those manifolds even back in the day.About the only ones useing them were for engines that Offy made Tunnel Rams for that no one else did.... like Oldsmobiles...If you think about it dividing the plenums on a Tunnle Ram in many ways defeats the purpose of them.TR's were designed for Hi RPM Power not low speed use....So by dividing the plenums you reduced the total amount of air that each runner could flow....

Divider in a tunnel ram won't help the performance in any RPM range. We did a bunch of experimentation with the Edelbrock TR-1 and TR-2 when they first were introduced in the late '60's. As was stated earlier, tunnel ram manifolds are designed to be effective at mid to high range RPM and I have yet to see one that offers performance increase below 4000 RPM. Divider only restricts the plenum flow and causes extreme turbulance at lower engine speeds.
You do see tunnel ram manifolds on T-buckets and yes, they probably do work OK on a 1700 lb. vehicle, but the advantage is only in aesthetic value.