Essentially in that regard all guards have that caveat. Jumping into guard is great for straight grappling competitions against two skilled competitors or where one might fear they would lose the take down battle. Jumping into guard any where else is not adviseable. Going into guard is a "oh crap, I am on my back in a bad position, how do I recover and get to a safe or dominant position" sort of thing.
That being said "Rubber Guard"
Pros:
1. It gives you a lot more control over the posture of your opponent then most classical guard positions.
2. It is derived entirely from a No Gi system, so it is applicable in MMA, and other No Gi situations with little to no adaptation needed.
3. It has a lot of unconventional submissions from it.
4. It allows you to have a lot of control while keeping 1 arm free.
5. When used together with a variety of flow techniques, it has a lot of ability to chain positions and submissions together.
6. It is a great way to set up Triangle chokes.
7. Of all guards you probably would absorb the least amount of punishment.
8. Very strong and great position to slow things down and rest.
Cons:
1. It requires extensive flexibility.
2. It requires you to be on your back, still able to absorb punishment. Essentially the same draw backs as any guard position.
3. It is a non dominant position, that requires a slow methodical approach towards setting up techniques, it is essentially a great "stalling" position. Due to this it lacks some dynamic approaches.
4. It's methodical nature makes it harder to improvise, if someone is aware of the system they know what is coming and makes it easy to defend.
5. Unlike other guard positions that are more "active" and allow for more dynamic sweeps and submission attempts, Rubber guard is more for control, and favors a slowed down approach.
6. Most of the "unorthodox" submissions chained off primarily of Rubber Guard are low percentage.
7. Most sweeps from Rubber guard are low percentage and not nearly as successful or numerous as many other guard positions.
8. Highly succeptable to "stacking" type passes and slams.
9. Controls upper body without a lot of control of the hips.
10. Difficult to use successfully on broad shouldered or larger opponents unless you have very long legs.
This is without getting into the whole "self defense" vs. "sport" aspect. This is purely a from a MMA and Grappling technical perspective.
My two cents.
Depends are you doing singles martial arts like Jiu Jitsu or judo or Kickboxing.
