The Nitecore TM11 is a light I used to own. I really, really liked it, only got rid of it because I got the updated version (TM26). It has extremely wide flood, so it is a great hiking or general purpose light. It is also lighter, more than an inch shorter, and takes four instead of three 18650s, so runtime should be better. I really like the voltage indicator also, rather than the dumbed-down battery level indicator on the DDR30. The TM11 has four modes, the DDR30 has only three. It has been my experience that the larger the light is, the more unlikely it is for me to carry it. So I would prefer the TM11 for that reason.
I can definitely see some advantages to the DDR30. The extra size might mean you can run it longer before it gets too hot, although I would have to test that to be sure. It is definitely a better thrower, so if your friend has lots of wide open spaces (hundred meters or more) the DDR30 will easily outperform the TM11. The DDR30 also has a better low mode, so if you need that, that is a deal-breaker for the TM11, which has a low of 200 lumens.
The TM15 and DDR30 are actually closer rivals. The TM11 is more of a flooder. For my purposes, the TM11 would make me happier, but your mileage (or your friend's) may vary.