They are exactly the same, keeping in mind the different concentrations. Ph drops are 5% and Miracle-Mineral-Supplement is 28%, so Miracle-Mineral-Supplement is slightly more than 5x more potent. So, if you want to try it, where the Ph Prime calls for 15 drops you could substitute between 2 and 3 drops of unactivated Miracle-Mineral-Supplement for the same thing.
Use 3 drops if you are using a standard glass dropper to measure, and 2 drops if you are using a regular MMS bottle with the dropper style top.
I used the ph drops from Innerlight for a long time, and now I use drops of MMS style concentration instead because it is so much cheaper. Although I also have a Jupiter Melody, and find the water from that to be very delicious, I still use the NaClO2 as an alkalizer because of the increased benefit of the cleansing from that.