Our district (public) uses TERC. However, I'm not sure my opinions would be helpful, because our district supplements heavily with locally-derived materials.
From what we have seen, I agree that it is light on practice and 'drill' in the early years of the program, but our schools were aware of this and I feel the (supplemented) curriculum offered here did a good job addressing this (too much for my kids, but they are outliers). There is also too much spiraling for our tastes, but again, my kids do not seem to be typical math students. There is also a fair amount of explaining and writing required; this was irritating at times but not an issue for my kids; they are comfortable writing and often enjoyed the opportunity to think more deeply. There was a fair emphasis on manipulatives, IIRC, but not sure if this was inherent to the program or our district; specific teachers used their discretion and my kids were not forced to use these if they didn't need/want to.
My biggest criticism is that there was no opportunity for acceleration or differentiated work, but again, I suspect this was district-specific, not TERC-specific. They do have challenge problems, which were often assigned to be thought about and completed over several days; my kids usually completed them during the class period in which they were assigned, if that tells you anything.
The general consensus here seems to be positive; our district consistently has some of the highest math scores in the state on standardized testing, including the new common core tests (take that as you wish). However, and this is a big however, the teachers did not use the materials exclusively, or even most of the time, depending on the unit, grade, teacher, etc. Also, our district has a well-developed program for math help, remedial and otherwise- it is tough to fall through the cracks.
