3hrs should not be a problem.
I went through FRA for work about a year ago with a 5hr turn around.
I needed to get through immigrations, go to baggage claim, pick up a case of equipment, go through customs, get to a hotel, set up my lights, photograph a subject, pack my gear , get back to the airport, check my gear through baggage claim.....and I still had almost 90 minutes to relax in the Business Lounge before my flight.
I have found FRA to be very "user friendly"