I found that when taking rose cuttings the conventional way ie a slit in the soil with a spade, sharp sand or grit in the bottom then insert cutting, never worked with me so last summer I began using the method above but using Perlite instead of grit. I took cuttings in July, November and again in February, keeping the compost moist, and have had a very high success rate, probably 90%. As you say they need a good year in the pot before potting up, plus a further year in their individual pots.