Springbar attachments for watch bands can be extremely secure, it depends largely on the quality of the pins used (this is how the straps on most high-end watches are secured, after all). But the actual implementation of the third-party springbar adapters... Of the handful I've seen, I've yet to meet one I totally love, as far as how they connect to the watch (always a little loose one way or the other).
The tube ones, on the other hand, always scare me; Apple's real ones I'd trust, because Apple's reputation is on the line, but the design bothers me, you've got extremely small screws that could gradually loosen/unscrew over a long period of time without you noticing, and once it comes loose, the result could be catastrophic. With springbars, the tension in the spring works perpendicular to the direction in which the strap is tugged - as long as there's enough tension in the spring to keep the bar extended a few millimeters into the holes on both sides, it's quite secure.