I had various tegus for some time. I agree they grow fast, that's why I recommended being ready to upgrade enclosures pretty soon. But a 40 gallon is perfect for a baby. Yes some Tegus can be feisty, but with handling the vast majority do remain very tame. Im not really sure what other lizards or monitors you could possibly have before owning a tegu, other than a beardie that would prepare you. Almost all other monitors of comparable size will be vastly more temperamental and harder to handle. I made this recommendation because the OP seems to have herp experience and a dedication to pet ownership. With knowledge and guidance there is no reason they cant have a gu.