I have been carbon dosing for a while for phosphate control. I do not have a nitrate problem (Knock on wood). It works very well for me. Carbon dosing in the past for me resulted in my last plenum turning into agrocrete, thus rendering it useless, and impossible to change.
I agree with you that a DSB are useful as a nutrient exporter, and can get a bad rap. They can be ticking time bombs if not cleaned just like a canister filter. The anaerobic bacteria need a carbon source in an oxygen poor environment to function for nutrient export. That is why I carbon dose my RDSB. If you read my post I went to the RDSB so that it COULD BE REMOVED from the system without having to remove all the critters. Since I have been using the RDSB for the last three months, the sand in my tank sand is very clean, and I am very happy. The RDSB takes the brunt of the nutrient export. I also point out the limits of the RDSB, and the necessity of using some other chemical treatment like ROWA Phos to completely eliminate Phosphates.
I have been keeping posting updated. If I find a problem with it then I will remove it, and report it on the forum. Anything in a tank not properly maintained can result in a tank crash.