The MemPlug MS is the exact same size and shape as the previous MemPlug CF and MemPlug SM. It sticks out slightly (less than 2mm) from the back of the Visor. These few extra millimeters of thickness are not noticeable and do not affect the Visor's fit in cases.
Unfortunately the Memory Stick is longer than the length of the springboard slot, so when the Memory Stick is inserted in the MemPlug is sticks out. Not a lot, just about 1/8". But, it's enough to make me uncomfortable. The pictures below show the Memory Stick fully inserted in the MemPlug. If you are using a flip-top case then you'll have some problems. If you want to keep the Memory Stick in the Mem Plug all the time, be sure to think about the feasibility of fitting your newly sized Visor into your lifestyle. I can't imagine how they could have done a better job fitting a Memory Stick into a Springboard.