i dont know the strenght of houdini book but when we look at the screenshot its look like houdini book strong in e4 line. analize for most popular opening like sicilian or ruy lopez and i think most of free public book on the forum did the same too. tuning their book with the most popular lines.
houdini book would have an extra database because its one of the latest book in release.
Japan Top team and hitman choose the road that people rarely through that way by using the shocking lines like 3.Be2 or 1.e3 not the stronger but strong enough to play around.
most of tour like sedat tour is using 3 minutes in time control, with fixed hardward specification.
Japan top team and hitman is very clever using that time control.
play the shocking line give the opponent out from the opening so the opponent just using their 3 minutes for the game and just seconds for one move analize only whille JTT and hitman have already prepared with their strong backup up line and variation for longger time in analize.
to judge which one is better i think it depends on how we play that book.i think in 3 minutes time control it could be a tight result for both (Hou book n JTT) but for longger time control i think houdini book stronger than JTT.
By time goes by i think someone will test it and realished the result...