eHarmony, is a 14+ years old obsolete site and a HOAX, based on a big scientific fraud, only sustained by big marketing budget.
eHarmony is a 14+ years old obsolete site using Big Five traits to measure personality of its members, but the Big Five normative test that had been proven/revealed as an incomplete and incorrect model to assess/measure personality of persons.
The Big Five normative test had been replaced by HEXACO or Big Six test.
Online Dating sites OFFERING COMPATIBILITY MATCHING METHODS BASED ON PERSONALITY SIMILARITY have very big databases, in the range of 20,000,000 (twenty million) profiles, so the Big Five model or the HEXACO model are not enough for predictive purposes. That is why I suggest the 16PF5 test instead.
The same applies for Personality Based Recommender Systems. Please see: "How to calculate personality similarity between users" Short answer: the key is the ENSEMBLE!
(the whole set of different valid possibilities)
Worldwide there are over 5,000 online dating sites, no one uses the 16PF5, no one is scientifically proven yet, and no one can show you compatibility distribution curves, i.e. if you are a man seeking women, to show how compatible you are with a 20,000,000 women database, and to select a bunch of 100 women from 20,000,000 women database.
eHarmony's algorithm is in the range of showing you 3 most compatible persons per 1,000 persons screened, and with the 16PF5 you can reach 3 most compatible persons per 100,000 persons screened; a 100 times more powerful algorithm (NOT 100% improvement, a 100 X improvement, really an innovation)