The Rabbetspace has the obvious advantage of even
pressure, but a bent point is only putting pressure on the edge of the mat package, in an
area in which should be well beyond the margins
of the sheet in the mat; so that should not cause
any problems. The one closing device that can
be seen to have provided uneven pressure is the
spring clip that is used with sectional frames.
The backing board, between some clips can be
found to have warped away from the glazing over time and strips of scrap board pressed into the hardware channel of the sectional frame will give more even support than such clips will.
Hugh