It is often said that Muslims who belong to insider movements are much like Messianic Jews. Messianic Jews are Jews who believe that Jesus was the Messiah, yet claim to remain Jewish, and do not normally call themselves Christians. In the same way, IM Muslims are following Jesus but within Islam.
So they say.
Little problem though: Most Jews don't believe that Messianic Jews are Jews at all. They are converts from Judaism to Christianity. Pure and simple--even if they are, ethnically, Jewish. Evangelical Christians are the only ones who, without reservation, accept that Messianic Jews are real, true Jews.
There is a good article on this topic by David Novak at First Things for anyone who would like to learn more. I suspect that we will find the same thing with IM Muslims--that eventually, their own claims to be real Muslims notwithstanding, the Umma will decide they are just misguided or deceitful Christians.
In other words, if insider Muslims are like Messianic Jews, it means the only people who really think they are Muslims are evangelical Christians, not fellow Muslims.