Why do you think developers should proceed with caution? They don't seem malevolent to me. Perhaps you question their methods, which is legitimate, but if you have any other information apart from that, I would like to hear it.
Additionally, I don't know if I can criticise their model. Yes, it's not very innovative, but on the other hand you can think of it as a outsourced European development team for US-based startups. They know the market, the language(s), the problems. They do the development work and then if the original startup wants to buy the product, they can. Who knows, perhaps it might even end up being not much more expensive than setting up the infrastructure and acquiring the knowledge required to operate in the EU. It might also serve as a test case: "is service X really going to work in the EU?". They take the risk that something might not work.
As an EU-based developer (who never used any of their products. yet?), I also think it's valuable for us (EU-based developers). Instead of waiting for startup X to get their act together, they offer us an alternative, which then later might be merged with the original product.
As a side note, there is a bit of a unintentional Schadenfreude to be found in this article as well. Since it's 6 - 7 months old, their investments in Facebook, Zynga and Groupon doesn't look so hot anymore as it did back then. Maybe they should avoid the investment side of things.
Generally speaking, I agree, but the Samwer teams often overstep the bounds and going beyond simply duplicating functionality (i.e. blatantly ripping the design features and html/css theme of the website landing page). I think if you talk to people who've worked for their companies (I have) there is the general impression that whatever the boundary is that should not be crossed, it is being crossed.
People keep saying "Stripe, come to Europe!" and "Why isn't there something like Stripe in Europe." A competent company with a track record of success finally builds a good approximation of the Stripe experience for Europe, so why should developers be cautious? Have they shut down companies when they haven't been acquired?
Also, I think it's a bit unfair to reduce the brothers to a "copy-cat" title. This happens everywhere, its just that they are the most successful at it. There are a lot of really cool tech companies in the valley that are relevant to non-english-speaking countries and developing ones but these countries don't fully benefit because the originators of the ideas pay no special attention to this countries. Mere providing different language translations does not breakdown the different albeit subtle differences between different cultures.
I think the samwers should be commended for what they do especially for their German market.
It's a mis-nomer that they frequently end up selling to the US company they cloned. Ebay and Groupon are about the only two examples.
Stripe would never, ever, ever acquire a clone like this. First, because the notion is already rare. But more overwhelming is Stripe's intense focus on creating its own culture and building its own stuff.