I had a TD-6 (I sold it) and a megadrum.
I have a DIY kit. It has 12'' mesh head pads. And the td6 worked very very well with rolls at all kind of velocities. Check out your DIY pad because it must be due to a bad assembly. Check your materials, your cone height and so on. My DIY pads worked great with the td6. Not the same happened with megadrum. Megadrum is a bit special module. You have to fine-tune it a lot and (dmitri, forgive me for saying this..) the td6 performs better with fast rolls.
I have found megadrum to work extremely well with piezo/switch pads (all of my cymbals) but it does not perform very well (maybe I have a not optimal configuration) with piezo/piezo pads (my snare and toms). Rolls are more consistent in td6 than in megadrum, although megadrum surprised me with its great sensitivity from strong to super-light hits (it can trigger all the hits made by a free bouncing stick, from the first hit till the stick is laying over the mesh head).
It is better to check it out for yourself. Both megadrum and td6 have their own advantages and disadvantages.
Megadrum has loads of inputs (I was able to connect all the pads of my huge kit). It performs quite well for being a DIY module, AND it completely beats the performance of low-end modules (Alesis, Fame, Millenium, ...) Despite not being perfect in its triggering (although it is improving with the time) it worths the money and effort it cost.
Roland modules (as the td6) have onboard sounds and you don't depend on a PC to make it sound. If you want to have a comparable to megadrum number of inputs (16 inputs), you will have to buy a high-end module (TD-12 (12 inputs) or TD-20 (15 inputs)) and spend over 1000 euros. Roland modules have a more refined processing of signals so they trigger them with better accuracy, but megadrum, with appropriate parameter tweaking, is very good also.
My piece of advise would be to have both! If you can afford having a Roland module.
You can connect to td6 the most delicate parts of a drum (kick, hihat and snare, and maybe toms) and leave the rest of the pads connected to megadrum.
I have now bought a TD-12 module on ebay. It is great and performs perfectly on rolls,even better than the td6. I don't want to through away my megadrum (I have put a lot of time in building it and I'm very fond of it) so it is going to be the partner of my roland module. Together they sum 2 mono inputs and 26 stereo inputs. Simply great!
