Statistics are always tricky, but according to some estimates there are about 330 million “oneness pentecostals” worldwide. For those not familiar with the group, their theology is that of classical modalism. This would not account for all the additional classical modalists in other traditions.
Given these numbers, it is interesting to note that classical modalists today outnumber JWs by about 42:1. I think that’s interesting given the fact that it seems like so much attention and energy in the church is given to combatting the heresies taught by the watchtower association, and yet I see relatively little directed against modalism.
Of course, if semi-modalism were included in these statistics, the numbers would be off the chart. But it’s worth noting that at least in terms of numbers the neo-arianism of the JWs is not nearly as big of a threat to the contemporary church as modalism is.