Rocker toe shoes, square toe shoes, standard shoes that are "set back", or any shoe type (rolled toe shoes, worn out shoes) that promote rather than retard breakover, reduce the effort needed to achieve breakover to varying degrees.
The belief that promoting early breakover shortens the stride is not, in my experience, well founded. While I have seen horses for whom the stride has indeed shortened while shod with a "breakover" shoe, they have few in number. The majority of horses shod with "breakover" shoes show some increase in stride length, sometimes a dramatic increase.
As with any horseshoe, the rocker toe shoe can be poorly fashioned and applied, causing lameness. I suspect the rocker toe shoe has been implicated in shortening strides when the shoe has been set in such a way that it puts pressure on sensitive tissues. I also suspect the shoe has been deemed ineffective when it has been fashioned with such slight "rocker" that little effect would be expected.