Howdy,
I run Eheims, and I have been for almost 30 years. Never a single problem other than the one filter that had reduced flow rate after two decades of 24/7 service - I finally replaced it. It's performance you can rely on. Search the Set-up forum for FX-5 maladies, and you'll find a laundry list of issues. Search Eheim, and you'll mostly find user errors of people new to canisters. Stick to the classic line and you'll save money in the long run because you know you'll get 20 years of use out of it.
I wouldn't know about Eheim customer service because I never had to contact them.
Just my $0.02
HarleyK