I believe the M on your soles/heels that came with your shoes denotes that they were cut for the medium width sole.
A medium Tri-Dex is about 1/4" too wide on my size 9 SST 6 LX. I opted not to trim it though.
The difference I have seen is that the standard H5 heel eventually became to grabby and I had to move to the H7 to keep my heel from stopping me too soon. The H7 was too much slide for me, so I bought a Tri-Dex and have been quite happy. It hasn't gotten too tacky yet, and I'm pretty sure it's seen more games than the original H5 did.
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"A word to the wise ain't necessary -- it's the stupid ones that need the advice." Bill Cosby
"Never argue with an idiot. They bring you down to their level and beat you with experience."