Those kinds of blades are not meant to be used with a mulch kit. Those are very similar to oregon G6 and G5 blades (though not as good as the g blades are), and Oregon has said many times over that they are for side discharging only. I use the G6's under my Z950 deck for part of the season (I mow for a living) and have for the last 3 years since they first came out so I do have some experience with them. IHTH
Thanks RG1, I appreciate your feedback.