Yes this is correct. I have a 258.08 from several years ago which does not have spin milled grooves nor a micro milled face. My short pitches did not spin the ball anywhere near my SM4s. Huge difference with any pitch and chip shots. Full shots with a wedge with worn grooves can drop and check the ball just from the drop angle of the ball being very close to vertical. You can tell the difference the milled face and grooves of an SM4 make in the 'touch' shots. 

I generally replace my wedges every year and 1/2 or so based upon the wear.  These clubs get a lot of use both on the course and in practice.  When I went from the "old" grooves to the SM4 grooves, I waited longer than usual because I believed the old grooves would still have better contact with the ball and I was apprehensive about switching to the SM4 grooves.

Once I made the switch to the SM4 grooves, I did not look back.  These had a much better grip on my ball than the older, worn grooves on my old wedges.  Based upon my experience, I would not be concerned with moving to the SM4 grooves as they were a definate improvement over the worn clubface on my older wedges.

As an added bonus, replacing the wedges gives me a chance to design new wedges from Wedgeworks.  If you have not done this before, I would definately check it out.