I bought my brother a pair of TDL nucleus 2s lately, but this is a completely different beast, from the company several changes of ownership later and a different philosophy (they're not at all bad, but that's another story).
RTLs were all transmission line designs, from the RTL1 standmount (my grandfather had a pair, at my direction after a dem... they were pretty good) through the RTL 2 (floorstander. I demmed these too and wasn't too impressed... bought the B&W 602s instead (also demmed mission's 751 and 733)), 3 and 4 (which added more drivers, longer transmission line and more money). I've not heard the larger RTLs.