I've come to the conclusion that mulching is a subject that should be discussed in context. Some grasses mulch more cleanly than others.
I don't have the mulch kit on my TTHP 52/19, but I do use a blade blocker. For the most part, I have no problem this time of year (mostly fescue for anyone who's paying attention) with mulching. Springtime is a different story, though. In the spring, I use low-lift blades and won't even think about mulching blades. During spring, the blocker is set to allow some discharge at all times and is wide open when circumstances permit.