"However, it has been claimed that 'Iglesia' are really far more interested in attacking Roman Catholicism than in carefully outlining their own beliefs and are therefore parasitic in approach, feeding off, and expanding through, disgruntled Filippino Catholics. The Philippines, of course, are overwhelmingly Roman Catholic (84% of the population) and Iglesia's undoubtedly great success in poaching members from that organisation is why, in the opinion of many, they were very slow to spread outside that corner of Asia.
Through it's magazine, 'God's Message' (formerly Pasugo) 'Iglesia' appears to heavily rely on anti-Catholic scare tactics as support for it's own doctrines, which cannot stand up to a careful biblical scrutiny. When purely outlining their own teachings, many cult-watchers have noted contradiction and inconsistency.
"From 1922, Felix Manalo started to teach his 'God's last messenger' doctrine (applied, of course, to himself). This was at a time of dissent and schism within the group and it was how he again centralized all power to himself and sought to make his own theological spin authoritative. Apart from being fervently anti-Roman Catholic, the group also rejects all other denominations and Christian-related sects, believing that true Christianity can only exist within their own group." -UKApologetics