I use one of these regularly and wouldn’t be without it. As far as “If you need a bead jack to mount your tires, you had better have it with you when you get a flat” is concerned, that hasn’t been my experience. I’ve had several tires — usually Continentals — where I needed a tire jack to get the tire on the rim, but the bead stretched out after that.
Most recently it was a set of Continental Sport Contact tires in 700x32c. I had mounted them a month or so ago and they were very difficult, even with the jack. I needed to dismount and remount them recently (changing from Schrader to Presta tubes) and it was no big deal — I just used a couple of blue tire levers.