I have both the DDM2 and the DDM3. Same machine but the DDM3 is higher powered and faster. The 2 cost £300 odds with a couple of 850 core bits and the 3 about £430 for the gun itself.
If you do a lot of drilling it is the best buy you will ever make.
My DDM2 was (ab)used daily drilling walls up to 4ft thick and pushed so hard i've had to wear gloves to hold it it was so hot and even pushed it with my feet. It refused to die no matter what i did to it and lasted 4 years before i the clutch gave in.
I got it repaired by a local diamond drilling company who service their own gear for £60 but as i use it daily and couldn't be without it, i bought the DDM3. It is different geared and has 3 speeds up to 3500rmp so of course i use it on speed 3 for everything regardless of what core size and what the makers recommend.