I have a Herm Sprenger prong collar and I love it! I went with the 2.5 mm. They're made in Germany.
I haven't used any other brand, but I know quite a few people who have bought the less expensive ones and every one of them has had the collar pop open. I don't know if it was the way they put it on or what; but I have never had mine pop open. It's smart to have a back up collar just in case.
I would think that Leerburg would want to sell a quality product. Maybe someone on here has one and can let you know what they think of it.
By the way, you have a gorgeous pup!