Even in Germany a convert isn't safe: their fellow immigrants can threaten or worse.
The pastor quoted in the article said that 90% of the converts kept coming to church, another measure of how serious the conversion was.
I think what we're seeing is a measurement of a minimum level of enthusiasm for Christianity in Muslim countries. Without harder numbers about the total number of immigrants I can't say much, but if Germany had 130,000 in the first 4 months and about 1/4 of them wound up in Berlin (wild guess from the routing of refugees described in another article), that's about 33,400 refugees in Berlin, from which one church added 450 members, or about 1.3%. Multiply by that 90% and get 1.2 as the minimum--and there may be other churches as well. These I think are the people who are serious about Christianity; there are probably many more who are interested but not willing to take the risky steps.