No, you don't need tubes with the spring bars. In fact, the spring bars are too thick to even try to use the tubes with them. The thing that tubes do is allow for easier strap rotation as there is less friction with steel/steel contact than there is with leather/steel contact. The spring bars rotate freely in the lugs, so you get the same effect as using tubes/screws. It all comes down to personal preference, IMO. I like the feeling that tubes (or spring bars) give. I will say that I've never had a lug screw loosen up because I wasn't using tubes, though.