I feel the Zoomatic is a good strainer that engages/disengages well - but they do have a couple issues:
The tension knobs are notorious for coming off. Not all do, but many do, and they're often difficult to find.
In addition to that, If the knob is tensioned too tightly, the seam in the tombstone body can spread open or break, or cause the wormshaft to deform metal shells
Also, the tension knob can gradually lose tension with hard playing and rimshots (but there's a fix for that)
Here's a fantastic resource of several pages regarding the various versions of the Zoomatic.
If you get a Slingerland with a Zoomatic , set up the snares so that the top of the strainer is well away from the shell when it is in the on position. By doing this you will avoid what many people do that damages the zoomatic in the first place.
One of the WORST strainers I've ever used. So much so, that I SOLD the 6.5x14 Sound King I had and never looked back.
That is, until the guy I sold it to was selling it AFTER he had replaced the Zoomatic with the Buddy Rich throwoff.
I DID buy it back from him, and it works much better and sounds every bit as good as it always did.