For every bad review on TripAdvisor there's literally 100 excellent ones, so I guess you're in the 1%
Good for you if you're in the 99% BEFORE having used them.
FYI the interesting thing with Tripadvisor is not the % of good reviews as many operators will use tripadvisor for their benefit, sometimes there are even fake ones (not saying it's the case for Dive Concepts) It is more from the bad reviews that you learn what's the operator is about since things are always OK, until they are not anymore, that's where you see why there are different levels of operators.
Here is an example of what happened a while ago with this specific operator, and it's not Tripadvsor :
Divers Missing in Bali
Also check for instance on TripAdvisor what is the best restaurant in your hometown and you will certainly have a laugh. This is for Tripadvidosr accurracy.
If you're looking for dirt cheap operators and the services that go with low budget, if you are not very regarding on the guides experience with the local sites, if you don't mind larger groups than the rest of the local operators who provide private guiding, if you prefer diving with unexperienced open water divers as buddies (Dive concept is mainly favored becuse of their cheaper certifications) then this might be for you. You'll probably enjoy I hope you will.
On the other hand regarding my different opinion :
Do you know where they are located and have you visited them in Tulamben, have you seen their dive groups underwater : I have on my part.
Have you used different operators in Bali? i have for the last 18 years.
Do you know what are the dive conditions in Bali? I quite do for the time i have been diving Bali.