I recommend it.

I had a Selle Anatomica and liked the slot, but the saddle itself was too soft for my liking. So I sent my B-17 to Monarch McLaren and got the cut out. I also had them put in their lining.



I punched a few holes along the bottom "skirt" and laced the saddle myself:


(Note - the photo is a little deceptive. That is NOT the angle that I ride that saddle: the bike, with sloping top tube is on a car rack. The saddle is actually a few degrees "nose up" on the bike)

This saddle is more comfortable, for me, than the B-17 without the slot, but it has not totally relieved the numbness problem. That being said, it's been on my bike for about 2200 miles now, and until I come into some money for something like a Selle SMP, it's what I'll be riding.