Hummdingers have a lot of uses. Slab with them, troll, cast at surface action and you can dead stick 'em in the Winter.
Mostly I use them when I believe the sandies are suspended in the area. Medium cast on a baitcaster and try different depth in the water column.
Another use is to re-locate a school of fish that have wondered off the spot. Fan cast around, slow roll it off the bottom and whammo. You can cover a lot of mid-depth bottom quicker than you can TM around looking with electronics. I find them quite often.
A must for any serious sandy/hybrid fisher.

what is comparable to the tnt slabs since they are no longer in production?

The six old geezers prunepicker slabs are identical to the TNT's and are a proven fish catcher. These are a substitute for the TNT's when they are not availible. His paint scheme is not as elaborate. I make some identical to the prunepicker for my own use and give a few to my best fishing friends.

Look Here

I used to have problems with 'em wrapping the line around the spinner but got some good advice here (I think from Ron C?), anyway ever since, nary a problem.......feather the line at the end of the cast so it stops short just before hitting the water, and raise your rod tip as you take up slack, then let it sink to desired depth. Also, make sure the wire holding the spinner and/or tail hook bends upwards very slightly.

TNT slabs & humdingers - I don't remember using anything else this year.