After not having time to brew for two months, I've finally been able to brew a couple more batches using my ThermoBarrel.
Temp loss was insignificant over a one hour mash.
On the second batch, which was the same recipe as the first one + 12 ounces of roasted grains. M+L efficiency was 72.8%, which is lower than expected.
The grist in the third batch consisted of 100% Rahr 2-row (19 lbs). For some reason, I had much less loss in this batch than I did in the first two. After meeting my pre-boil volume target, I collected another 3 quarts of wort. M+L efficiency was 72.3% (not counting the extra runoff).
As shown in the image below, 19 pounds of grain with a water:grain ratio of 1.35 exceeded the upper limit of the unit if you want to use the recirculation port.