In this video at around 22 minutes Fr. Pfeiffer claims Ridgefield has lost 100-200 faithful to the indult and Post Falls 300 to the indult.
On the other side of the coin, from my observations, since the lifting of the excommunications I see the new people coming to mass are Novus Ordo types that want the SSPX to be regularized so they can come without reservations to the SSPX mass. They come because our high mass service is well orchestrated, and it is the closest most convenient Latin Mass.
Therefore, the faithful leaving the SSPX for the indult, may be offset by the Novus Ordos and indulters coming from outside of the SSPX. As far as who loses people, the SSPX or the Indult mass centers, it will all depend on who is more of a convenient drive for the population centers. And who has the prettiest church, prettiest mass, the best breakfast, the most after mass recreation (basketball tennis volleyball courts, swimming pools, parks, etc.). Just like the Protestants they will have to compete to get the clientele.
If the sermons (doctrines being taught) are the same why would any accordista favor the SSPX over any indult mass?
The pro-accord "SSPXers" think that it will increase the attendance by "legitimizing" themselves, but the other side of the coin is that they will loose the people they have to the indult mass and the Resistance. They will become salt without flavor.