Some of it depends on lifestyle, but I wear a two-piece system, so I wouldn’t feel comfortable taking my chances without a belt; I’d be too afraid of the two pieces detaching.
That said, I’ve started wearing the StealthBelt Pro, and it’s been an absolute game-changer. I have an active job as a paramedic, and I do a lot of sports like SCUBA diving, skydiving, etc... and IMHO the StealthBelt is infinitely more comfortable, secure, and aesthetically appealing. I also love how you wear the bag horizontally above the belt-line. Since I wear uniform pants with a duty-belt with a heavy radio on it, wearing the bag in the usual vertical position would’ve been extremely uncomfortable, if not impossible. Wearing it horizontally in the StealthBelt also distributes the weight better, so it doesn’t feel nearly as heavy.
like I said: game changer.