Sorry to rain on everyone's parade, but...
I remember other threads from on here where the 35mm mounts were slated and the 120 ones deemed ok. I have the V750, and do not (generally) have this problem. I therefore find the OEM mounts perfectly OK for my needs. There are lots of ways in which poor results, note I use the word poor deliberately, can be obtained using these scanners. Getting good results OTOH does require patience, but once a workflow has been arrived it can be achieved consistently.
I feel that on this forum overall, there is far far too much obsessing over 'sharpness' and not enough on other equally important components of what makes a picture 'good' as opposed to 'poor'
Oh well, I expect some backlash from this post, but I feel the point had to be made. By all means, spend the money on these mounts. If you are doing a lot of scanning, or most of your film stock is curly, it may be helpful. However, I feel that greater changes can be made by paying more attention to other aspects of the workflow.
Regards to all
Andy