what do you mean by "good" and which DC header are you talking about (JDM or USDM)?
my article here puts the DC in perspective compared to the others.
for a massed produced aftermarket header they make average power gains. Among the smaller USDM headers with 2 in. collectors, they are quite good (Oct 1999 Sport compact Car header test on a GSR with an AEM CAI and Greddy Evo exhaust and stock cat).
The welding is not the same quality as a custom TG welded header.
You can find headers that make more power over certain parts of the powerband. The DC JDM 4-1 with 2.5 in. collector is as good as the JDM ITR (Spec R 98) header.
Again, the top end headers with a hybrid design layout and 2.5 in. collector will make a lot more power when mated with a 2.5in. collector and 2.5 in. exhaust.
You choose and size the header layout that will achieve the power goal you want and where along the rpms you want the gains. Now that we have hybrid header layouts available, the old 4-1 = peak power gains AND 4-2-1 = mid rpm power gains is NO LoNGER TRUE.
Please check out the header tech articles here if you haven't already.
we try not to rehash these sort of old basic questions you can get answered on any Honda board like a beginner's board such as Superhonda.com. In the future here, can you please search first on the forums using the search function on the lefthand side of the webpage to see if it has been already answered. That would be very much appreciated by all here. thanks