As you can read in the manuals i posted it is necessary to cap the max-bandwith a little for QoS to be able to work. This is also mentioned in the discussion garys_2k posted before.
Well 20% generally is a very high value which isn't required in most cases. Commonly 5-10% is way enough to get QoS run smooth. In general, as smaller your real speed provided by your isp, as more you should cap (up to 20%)!
On the other hand, how would you know that your tp-link or asus firmware internally do not cap the max-bandwidth you entered without your knowing? Just for prevent their users for making a common mistake of beginners configuring QoS.
Here an example how tomato suggests how to set your max bandwidth (»tomatousb.org/tut:using-tomato-s-qos-system
- Section Bottleneck No1:
If your PC('s) can be slowed down so that they send data to the
router at a slower rate then your router can send it to the ISP,
we ensure that there will always be some free space in the
buffer. This is the reason I recommend you to set the
Max Outbound" bandwidth in QOS-BASIC to
approximately 85%, or even less, of the maximum
real (measured) uplink speed.
You see the pattern here? Your argument is delusive. I don't impute you act in bad faith, just allude to your lack of knowledge regarding this topic.Anyhow, back to topic:
DD-WRT's and Tomato's QoS basically follows two different philosophies.
During Tomato tries to get their users as much control about the mechanism as possible, DD-WRT tries to offer their uses a easy to use QoS which doesn't require a major knowledge about the functionality of QoS in general.
In fact, Tomatos implementation is much more flexible and allows complex scenarios which can't achieved by DD-WRT's solution just like that. But this comes in lack of its usability. A well configured QoS requires a deeper knowledge about how the mechanisms of QoS work in the background.
DD-WRT's QoS on the other hand allows unversed users to achieve their commonly simple requirements without the need of studying long manuals and much theoretical stuff about traffic shaping.So in conclusion:
If you have complex requirements to the bandwidth management and don't fear to struggle with long manuals Tomato might be the right choice for you.
But if you have only simple tasks like limit that and that ip-address or prioritize my voip-calls over my children's torrent use, and all this without much effort, then DD-WRT is the better approach