When contacting Omron customer service, they were of no help at all, a woman telling us their machine was not adjustable, of which we inquired, that my BP was probably correct on the Omron and that I should check with my doctor. I did and learned the Omron was wrong (over 20 points higher than by actual BP) when compared to the doctor's office sphygmomanometer. Let me emphasize, it is the latter that you should always compare your home unit with.
Checking with my primary care doc, I found their office used a Welch Allyn sphygmomanometer, so I purchased their home model. Same problem, but great customer service with WA. They even went so far as to replace their product free, even after I purchased it from Amazon. But it's all for naught since I recently learned the Welch Allyn was off an average of 34 points too high. The doc took the BP several times and in both arms.
The scary part of this is that for at least three years now I have been fooling myself thinking my blood pressure was significantly high. It isn't, but it is high enough to require some BP medication to keep it under control. Based on my experience, the only way I would use one of these home BP meters is to first check its accuracy with your doctor, then proceed based on those results. In my case with the Welch Allyn, I will simply subtract around 34 points from each reading.