I couldnt really tell you without testing them personally, but several guys on here have found the exhaust cam to be inadequate.
By having a tuned exhaust diameter and length can help extract exhaust gases more efficiently and allow you to use smaller valves or less valve lift, there are several reasons for doing this , and to put it simply the less exhaust gases that get blown back into the engine the more efficient it is and the less fuel expended without burning going through the exhaust also means better efficiency. Its a little more complex than I stated but it may give you an idea.
By cutting down on the time that the exhaust valve is open reduces the amount of wasted fuel and also reduces burnt gases re entering the engine, but it has to be big enough and open enough to do the job.
Without physically testing the exhaust cam it is hard to determine wether it is an improvement or not but others have tried it and seen no gains in power , where it may help is in power delivery and better throttle response.
Garth has tried the exhaust cam and found no improvement on the dyno.