Durability and Test Results

How durable is this chain guide?

Of corse it is weaker than most heavy-duty downhill/freeride chain devices.

If there will be a strong direct hit by rock into the chain guide cage during a crash, then it will break.

Another dangerous situation is then your chain falls off (for example after a big crash) and gets stuck between a chainring and a guide cage. And if you just start pedalling with all your weight without placing the chain back then it will break. So inspect your bike after any crash, not only to save the chain device, but also to detect other problems that can cost you health.

And if it breaks you still can try to glue it.

For not so strong hits everything is much better: material will flex and withstand the impact.

Test results

This is my test setup:

Usually, I ride local foresty trails with a lot of bumpy roots and some jumps/drops.

Chainring

32t Shimano Deore ring. Not a special single-ring with high or narrow-wide tooth pattern. Just a heavily worn basic multispeed ring.

Chain

SRAM PC-991. Again, heavily worn.

Rear derailleur

Shimano XT M772 Shadow Medium Cage. No Shadow Plus/TYPE 2 derailleur with additional chain stability.

Looks like almost worst case setup for a chain guide device, isn't it? And still I've experienced only rare chain falls: after a huge crashes and sometimes during a back-pedalling on a rough terrain.

Back-pedalling issue can't be solved by this chain guide with only top cage (the chain comes off from the bottom of the chainring). Bottom chain roller/slider or a special chainring with narrow-wide tooth pattern will do. Or you just can avoid back-pedalling on a bumpy trail :)

In all other cases everything is fine.

Here is how it looks like after a month of mud riding:

It's unpainted so in wet and muddy conditions it can become dirty very quickly. You should consider painting it if rains are regular on your trails.