Actually, they are almost identical in structure. Tbol just has a 4-chloro alteration which keeps it from converting to anything (like estrogen).
Of course this changes its A:A ratio and a few other things, but it is certainly not an unfair analogy.
I've used Tbol and Var in the same cycle and preferred Var. Tbol gives better fullness (like Dbol with an AI, minus the androgenic sides

), but not as much in the way of definition or vascularity as Var. Also, Var is great for injury repair, which is all I use it for anymore. It makes road rash and surgeries (I ride a motorcycle) heal up much faster than normal.
Tbol actually lowers your blood's clotting ability (like a blood thinner), which can be dangerous if you hurt yourself. Just knicking yourself shaving turns into a 10 minute bleeding ordeal.