Converters are not expensive or sophisticated, but quality can still vary quite a bit. I've used inexpensive Chinese converters and they work OK. In general, a name brand such as Schmidt is going to be a bit more expensive, but it is less likely to have problems. I suggest staying away from the inexpensive all plastic models. PSI offers two versions - the more expensive version is fine and works well, but I've found that their less expensive converters tend to be a bit leaky.
A point that should be emphasized is that you need a 'standard international converter'. Schmidt is a well-respected German manufacturer of pen components who happen to make standard international converters. However, not all 'standard international converters' have a prominent brand name. In fact, many converters with a prominent brand name are actually proprietary and fit only pens made by the same company. Looking for a converter at Amazon can be confusing because they randomly mingle standard international and proprietary brands. This is another reason to opt for a supplier like Goulet - fountain pens are their only business, and they understand the market and the options very well and can help you select a converter that will fit your pen. That said, there are a few other well respected fountain pen companies - Vanness, Dromgooles, Goldspot, Anderson Pens, nibs.com, etc.