I have used Quest Central for DB2 and it is one of those very frustrating products that have some good bits mixed in with aspects that are rubbish. e.g. The Compare tool to compare one schema in say Prod to it's equivalent in Pre-Prod and can prove very useful in detecting variations. However support for Sequences is virtually zero.
Moreover, having experienced several release of the product over time, and raised numerous bugs with Quest, I have repeatedly found aspects fixed in an earlier version returning to haunt you. I have also spoken to their lead developers in the states about aspects I would like to see, promises made but not delivered.
Most recently Quest seem to have ditched the Quest Central direction in favour of Toad for DB2, probably tied to their dispute with CA over the origins of some of the source QC code.
Having seen Embarcadero's demo, it seemed a much more rounded product and supports things Quest ignored (e.g. Sequences). If you are going to check out any products, I would personally suggest avoiding Quest.