Price was certainly a factor when i bought the CD+, along with wanting minimum level 5 PP. At around £10 a hoop at the time, i considered them a great deal. They were also the Reflex ones. Clearance at Chain Reaction i think.I've found Marathon Greenguard to be a very easy-rolling tyre, and comfortable if some experimentation is done with pressures. My old 531 Dawes Jaguar has these in 28 mm and for poor roads littered with debris they are probably the best compromise of p*ncture resistance and weight. I've not felt the need to "go nuclear" with M+.
DC+ in 35 mm wide make very good tyres for general purpose bikes such as a flat bar hybrid. I'm running two sets currently and the tyres were cheap enough @ £12 each. However, I'm not seeing such good offers on them recently compared to a year ago.
In terms of running cost per mile, Marathon Greenguard are probably the most economical tyres you can buy, because they last up to twice as long as nearly everything else. Marathon uses a harder wearing compound and a higher TPI carcass (67TPI vs 50TPI on Delta Cruiser) and I perceive them to roll slightly easier than DC+ if anything.
I'm now running a set of 38 mm Marathon on a Raleigh Hybrid and they are both comfortable and easy-rolling. I got them at under £16 a tyre and decided to get some to experiment with the biggest 700c size of Marathon.
In future, if I can get Marathon Greenguard at a good price when on special offer, I will be buying these in place of Delta Cruiser+, although I will probably stick with 35 mm and not bother with 38's. They seem to add more weight than they add comfort and also reduce mudguard clearance so mud & plant life debris picked up riding on woods tracks etc will sometimes get caught in the gap between tyre and guard and make an irritating noise.
Good to know the difference between CD+ and MG, and although mileage is not a big deal to me, if there's not a lot in the price between them, i'll try MG next time.