Having had the Truxedo Lo Pro QT now for about a month now I am happy to say that I do not regret having opted for a soft cover. While not as secure as the hard covers, it is still relatively secure and it has not leaked at all (even in severe rain).
I suspect it may have improved fuel economy slightly. Last week the onboard computer revealed 10 l/100 km on a return trip from London to Oakville. I have done even better than this previously but last week it was -14, windy and, of course, I have Blizzak DM-V1s installed.