I have two of them, both standard models. Would love to get a target model. Like all the .22 autos I've had, or shot, they are picky about the ammo. They may only shoot one brand/load well, or they may shoot all but one brand/load well. Each one is an individual, or so it seems.
MY first one runs well, is fun to shoot, and has nicely hand checkered grips, (done by a friend of mine).
My second one was in a local shop, where they said they tried to use it as a range rental gun, but it was a jam-o-matic. I bought it anyway ($140, IIRC), and sure enough the first mag I shot, it jammed a few times. Then I OILED it, and it ran like a fine sewing machine.
They are true Lugers, in the legal sense, but share only a resemblance to the P.08, and are not a precise copy of the mechanism.
I recently obtained a NIB (unfired) stainless steel Luger, made in the USA, marked Stoeger and Luger. and yes, its a 9mm, P.08 clone.
The Erma guns were not great. Not total junk, but not great. They used a large amount of alloy parts, and have a reputation for failing. And repair parts are non-existant. Besides the .22, they made a neat 3/4 scale Luger in .380ACP. I passed on one of those at a show recently, due to concerns over its durability, and mostly because it was outrageously priced.
All else being equal (and it almost never is) bigger bullets tend to work better.