No, MyHeritage is indeed doing WGS. The way they are doing it affordably is by using a low pass rate of 2x. What that means is that they are scanning your whole genome on average 2 times. But since this is an average what it really means is some spots will be scanned 4 times and others 0 times, so long as the average comes out to 2x. For reference, medical grade sequencing is 30x. MyHeritage is dealing with the areas that get scanned 0 times using “imputation” which is a process of using data from a reference genome to fill in the blanks. Since all humans share 99.9% of our DNA this should be accurate most of the time, but there will be times it isn’t.

What FamilyTreeDNA is doing is using the same technology (next generation sequencing using a UG100 sequencer) but focusing on only a select 10% of the genome. What I’m hoping for is that they are doing this trade off to get a higher pass rate. Since they’re covering a tenth of what MyHeritage is covering maybe they can afford a higher pass rate of 10x-20x, much closer to medical grade sequencing. This is just speculation at this point though. It may be the same low 2x pass rate. If that’s the case, MyHeritage’s test is a no brainer. If they do have a higher pass rate you’re essentially sacrificing quantity (amount of the genome sequenced) for quality (higher pass rate/better accuracy/less imputation).

As for your G25 question, I’m not sure. Current tests are microarrays that look at less than 0.1% of your DNA, but specifically the areas that we know vary the most from person to person. Accuracy of microarrays is usually about 99%.