Many designs of anti chain-suck plates have been made. Most types do not prevent actual sucking of the chain. When they work correctly they do prevent the final gruesome wedging of the chain into the chain-stay, and thereby also forcefully knock the chain free from the teeth to which they are "stuck" by friction, mechanical resistance, and chain-load. One particular design has a more gentle action where the chain rollers are continuously prised free from the bottom teeth of each chain-ring ; it therefore stops sucking soon after it initiates.
These devices can prevent 1-ring and 2-ring suck when they work properly.
However, all types of the device need very strong attachment to the chain-stays (eg welded, brazed, or riveted nuts) because they can be subject to high forces, and also require regular fine adjustment to be very close to the chain-ring teeth. Clamps are unreliable for attachment. The average bike shop does not have experience in fitting these plates, and the problems which can occur. Malfunctions are common.
On mountain bikes, the chain-rings are unavoidably subject to abuse. If the chain is allowed to get past the plate (by poor adjustment, by damage to the chain-rings, or by unreliable mounting of the device) then the problem can be worse than if no plate was present. Severe damage can occur to the chain-stay, chain-ring(s), and chain. It can also be extremely difficult, on the trail, to free a chain jammed behind an anti-suck plate.
For the specific case of bikers who are knowledgeable about the issues, maintain their own bikes frequently, and know how to install and adjust the anti-suck plate properly, it may be a suitable solution.
However, anti chain-suck plates are not recommended as a general solution.