We've used it in my school for the first time this year. Reception run it differently, as do Y5 & Y6 (TAs run Fresh Start with those who need it) but Y1-Y4 all have 20 minutes daily phonics.
Finding sufficient teaching spaces, getting all the children assessed 1:1, spending a fortune on frogs etc. have been the main headaches but it has been a great success in terms of helping children to catch up. At the start of the year only 16 children from Y1-Y4 were assessed as being ready for a spellings group, at this point in the year we have 7 spellings groups. All children are assessed half-termly in addition to those who are struggling receiving 1:1 for 10 minutes a day (usually in the afternoon).
The composition of the groups changes each half-term with the exception of the spelling group children as there is no assessment process for that part of the scheme (we have just produced our own though as we found that some capable readers are struggling to keep up with the spelling activities).
It requires a highly organised person to be in charge of the running, assessment and fielding the complaints from people who've been given too many hard to manage children in a single group. I've enjoyed teaching Y2-Y4 in one group and know that the children have too. We have tried to be sensitive to the feelings of Y4 children who are in groups with Y1 but have found that the spellers and higher phonics groups don't mind about the composition, it's Y4 children who are on level E with Y1 who object. Where possible we've provided 1:1 for these pupils but, in some cases it has been used as a motivational tool (where the lack of progress is down to lack of participation rather than because they are trying but it just isn't working for them).
For my own class the RML scheme has been what they needed however, as a KS2 teacher, I would be reluctant to deliver it in place of regular literacy lessons.