I've done a lot of synching using both products interchangebly. I use whichever one is cheaper (usually using a few hundred doses each year), and sometimes it is the Estrumate, but more often than not it is the Lutalyse. I do like the 2 cc dose better so if price is close I use the Estrumate. We have not had any issues; our response rate is right where it should be on cows (about 2/3 response for one shot) and our conception is 70-80% breeding on observed heats. I have not noticed any difference between products. I use 2 cc for Est. & 5 cc for Lut. Having said that, this is product bought in Canada, and our drugs could have different strengths due to licencing requirements. I know that our CIDR's had more active ingredient than the ones in the US at one point, and maybe still do?
As was mentioned earlier heifers are a different question. I have had varying success with PG's on heifers, even using a two shot system. Yet I turn them in with a bull and they mostly breed first cycle. There are a few things to consider; sexual maturity, the heifers naturally synching heats with each other and the shorter estrous cycles of most heifers versus cows. Most of these systems are set up with the assumption of a 21 day cycle. It is not uncommon for the heifers I have worked with to have 14-17 day cycles, and uncommon for one to hit 21 days.