As I said I've never flown FR but I didn't criticism them either.
From what I have gleaned here and on other aviation sites, when things go well, say 99.5% or more of the time, you will be a happy camper.
But in the less than 0.5% when things go pear shaped you are on you own. I'm not referring to safety issues but when they have to cancel a flight. They could care less about assisting you to complete your journey. "Here's your money back" is their idea of customer service.
Now this probably wouldn't matter at Krakow where there are other options (albeit expensive) but at Hahn?
I'm not saying it has never happened but have you ever heard of FR rerouting/rebooking on another airline?
You are unlikely to encounter a problem with FR, and I don't think there are any questions about their safety. But any FR traveller should expect to be left high and dry if/when things go wrong.